A Slovenian international, Dončić made his senior debut for Slovenia in 2016 at only 17 years of age; he would later be named to the All-Tournament Team after helping his country win its first EuroBasket title in 2017.
According to his family, Dončić first touched a basketball when he was seven months old, and by age one, he was frequently playing with a miniature hoop in his room. He played a variety of sports in his childhood, including football, which he later quit after growing too tall. At age seven, he began playing organized basketball at primary school in Ljubljana. His opponents at the time were up to ten years old, as Dončić reflected: "I was always training and playing with older kids who had much more experience than me. Many of them were bigger and faster than me too, so I had to beat them with my brain." He admired Greek basketball player Vassilis Spanoulis from his early teenage years, stating that he was "enchanted" by him. He wore the number 7 at Real Madrid in honor of Spanoulis. Dončić also grew up admiring American basketball player LeBron James.
When Dončić was eight, his father started playing for his hometown club Union Olimpija, and Olimpija Basketball School coach Grega Brezovec invited Luka to practice with players of his age. Dončić was initially expected to practice with players his age, but only 16 minutes into his first training session, the coaching staff moved him up to the 11-year-old group. Starting in the next session, he primarily practiced with Olimpija's under-14 team, but due to league rules, he only played for the club's under-12 selection team, coming off the bench against opponents three or four years older than him. Despite his exclusion from under-14 games at the time, Dončić often asked to attend practice, even when his coach asked him to stay home.
Representing Olimpija at the under-14 Vasas Intesa Sanpaolo Cup in Budapest in September 2011, Dončić was named the most valuable player (MVP) despite finishing as runners-up to FC Barcelona. In February 2012, he was loaned to Spanish club Real Madrid for the Minicopa Endesa, an under-14 Spanish club competition. Dončić, who was among the youngest players on his team, averaged 13.0 points, 4.0 rebounds, 2.8 assists, and 3.3 steals per game to win tournament MVP honours, leading Real Madrid to a second-place finish. In April 2012, he took part in the under-13 Lido di Roma Tournament for Olimpija, finishing as MVP and leading scorer with 34.5 points per game. In the semi-final round of the event against Victoria Fermo, he posted 29 points and 15 rebounds. In a title-clinching win over Lazio, he erupted for 54 points, 11 rebounds, and 10 assists.
Dončić is interviewed after a youth game with Real Madrid in May 2014.
In September 2012, at 13 years of age, Dončić signed a five-year contract with Real Madrid, immediately standing out on the under-16 team with coach Paco Redondo. He moved to Madrid, living with football and basketball prospects. In February 2013, Dončić led Real Madrid to a Minicopa Endesa win, averaging 24.5 points, 13 rebounds, 4 assists, and 6 steals per game. In the final game of the tournament, he contributed 25 points, 16 rebounds, and 5 steals to defeat FC Barcelona and win MVP honours. In March, Dončić earned MVP accolades of the under-16 Spain Championship, scoring 25 points in a championship game win over the Gran Canaria youth team.
In the 2014–15 season, Dončić mainly played with Real Madrid's under-18 team and reserve team. With the reserve team, he averaged 13.5 points, 5.9 rebounds, and 3.1 assists, helping them win Group B of the Liga EBA, the amateur fourth-division of Spanish basketball. By the end of the season, he earned all-league honourable mention accolades from the basketball website Eurobasket.com. In January 2015, Dončić won the under-18 Ciutat de L'Hospitalet Tournament and was selected to the All-Tournament Team, despite being two years younger than the rest of the team. On January 6, against the youth team of his former club Union Olimpija, he posted a double-double of 13 points, 13 rebounds, 4 assists, and 4 steals. In May 2015, he also won the under-18 Next Generation Tournament, for which he was selected MVP after helping defeat defending champions Crvena zvezda Belgrade in the final.
On April 30, 2015, Dončić made his professional debut for Real Madrid in the Liga ACB against Unicaja, making his only three-point attempt in under 2 minutes of playing time. At 16 years, two months, and two days of age, he became the youngest player to ever play for Real Madrid in the ACB and the third-youngest debutant in league history, behind only Ricky Rubio and Ángel Rebolo. He played five games in the 2014–15 ACB season, averaging 1.6 points and 1.2 rebounds in 4.8 minutes per game.
In the 2015–16 season, Dončić became a regular member of Real Madrid's senior team. He played against the Boston Celtics in an NBA preseason game on October 8, 2015, collecting 4 rebounds, 1 assist, and 1 block. On October 16, at age 16, he debuted in the EuroLeague, scoring 2 points in a loss to Khimki. Dončić became the 21st player ever to debut in the EuroLeague before turning 17. On October 18, he recorded 10 points and 4 rebounds in a 94–61 win over Gipuzkoa. On November 29, Dončić posted a season-high 15 points, 6 rebounds, and 4 assists against Bilbao. With the performance, he set a new ACB record for most points and highest Performance Index Rating (PIR) in a game for players under age 17. He scored 12 points and grabbed 5 rebounds on January 7, 2016, against CSKA Moscow in the EuroLeague. After a Real Madrid time-out in the second quarter of the game, Dončić made three consecutive three-pointers, recording 9 points in 2 minutes. Through 39 games in the 2015–16 ACB season, he averaged 4.5 points, 2.6 rebounds, and 1.7 assists. In 12 EuroLeague games, he recorded 3.5 points, 2.3 rebounds, and 2 assists per game.
Dončić shoots a free throw for Real Madrid in January 2017.
Dončić made his 2016–17 season debut on September 30, 2016, against Unicaja, recording 6 points and 4 assists in 19 minutes. He collected 3 points, 5 rebounds, and 4 assists in an NBA preseason win on October 3, 2016, over the Oklahoma City Thunder. On December 4, he posted a double-double of 23 points and 11 assists, both season-highs, in a 92–76 win over Montakit Fuenlabrada. The game earned him his first ACB player of the week honors. Dončić scored a team-high 17 points in a EuroLeague victory over Žalgiris Kaunas on December 8, 2016. After recording 16 points, 6 rebounds, 5 assists, and 3 steals in a 95–72 win over Brose Bamberg on December 22, he was named MVP of the Round in the EuroLeague, becoming the youngest player ever to do so. He earned the same honor on January 14, 2017, after posting 10 points, 11 rebounds, and 8 assists to help beat Maccabi Tel Aviv. On February 9, Dončić recorded 5 points, 7 rebounds, and 11 assists to defeat UNICS Kazan. He scored a season-high 23 points on February 18, in the Spanish King's Cup versus Baskonia. After scoring 13 points and grabbing 8 rebounds in the 2017 EuroLeague Playoffs against Darüşşafaka on April 26, he shared MVP of the Round accolades with two other players. Two days later, he won the award outright, posting 11 points, 5 rebounds, and 7 assists to lead Real Madrid to a EuroLeague Final Four berth. Through 42 ACB games in the season, Dončić averaged 7.5 points, 4.4 rebounds, and 3 assists, and through 35 EuroLeague contests, he averaged 7.8 points, 4.5 rebounds, and 4.2 assists per game. He was named EuroLeague Rising Star by a unanimous vote and also claimed the ACB Best Young Player Award.
Dončić assumed a more significant role for Real Madrid entering the 2017–18 season, after the team's star player Sergio Llull suffered a torn ACL during EuroBasket 2017. In his season debut on October 1, 2017, he recorded 8 points, 6 rebounds, and 4 assists in a 94–88 victory over MoraBanc Andorra. In his first EuroLeague game of the season, on October 12, Dončić scored a career-high 27 points to help defeat Anadolu Efes. In his next game, he nearly recorded a triple-double against Valencia, with 16 points, 10 assists, and 7 rebounds. On October 24, Dončić was named EuroLeague MVP of the Round after erupting for 27 points, 8 rebounds, 5 assists, and 3 steals. He was named MVP of the Round again two days later, eclipsing his career-best with 28 points in an 87–66 win over Žalgiris Kaunas. Dončić also grabbed 9 rebounds and had 4 assists in the game. At the end of October, he earned EuroLeague MVP of the Month honors, becoming the youngest player to win the award. On December 8, he set a career-high in scoring, with 33 points, 6 rebounds, and 4 assists against Olympiacos Piraeus. Dončić led Real Madrid to a 79–77 victory over defending EuroLeague champion Fenerbahçe Doğuş on December 28, contributing 20 points, 10 assists, and 8 rebounds. Following a 24-point outburst in 22 minutes versus Movistar Estudiantes on December 31, he was selected as Player of the Round in the ACB. He was later named ACB Player of the Month for December, becoming the award's youngest recipient ever.
(left) with Real Madrid; (right) guarded by Josh Adams
On February 9, 2018, Dončić led his team with 27 points in a losing effort to Olympiacos, 80–79. He had another strong performance on February 17, versus Iberostar Tenerife in the 2018 Spanish King's Cup, posting 17 points, 7 rebounds, 5 assists, and 4 steals. On March 30, 2018, Dončić scored 24 points, grabbed 9 rebounds, and made a game-winning three-pointer with under a second left in regulation to beat Crvena zvezda Belgrade, 82–79. On May 9, he recorded 17 points, 10 rebounds, and 10 assists in 22 minutes against Real Betis Energía Plus, for the first triple-double in the ACB since the 2006–07 season and the seventh in league history. Dončić finished with 16 points, 7 rebounds, and 2 assists on May 18, in a 92–83 win over CSKA Moscow in the EuroLeague semi-finals. On May 20, he guided Real Madrid to a EuroLeague finals victory over Fenerbahçe Doğuş. He was subsequently named EuroLeague Final Four MVP after scoring 15 points. Dončić won the EuroLeague MVP award, being its youngest winner, after averaging 16 points, 4.9 rebounds, and 4.3 assists per game over 33 EuroLeague games and leading the league in PIR. He also repeated as the EuroLeague Rising Star, becoming the third back-to-back winner. Also, Dončić earned the ACB Best Young Player and MVP accolades after helping his team defeat Kirolbet Baskonia in the league finals. On June 29, 2018, he parted ways with Real Madrid.
On June 21, 2018, Dončić was selected with the third overall pick by the Atlanta Hawks in the 2018 NBA draft. He was then traded to the Dallas Mavericks in exchange for the draft rights to Trae Young and a protected future first-round pick in 2019. After the draft, Mavericks head coach Rick Carlisle said, "At one point, we thought there might be a slight chance Dončić could fall to us, but a couple of days ago it was pretty clear that there was no way that was going to happen. He's just too good. We get a guy we think is franchise foundation piece." He signed his rookie contract with the Mavericks on July 9, 2018. Dončić did not play at the 2018 NBA Summer League due to his late buyout from Real Madrid. Before the 2018–19 season, ESPN considered him to be the favorite to win the NBA Rookie of the Year Award.
Dončić made his regular-season debut on October 17, 2018, recording 10 points, 8 rebounds, and 4 assists, in a 121–100 loss to the Phoenix Suns. On October 20, Dončić recorded 26 points and 6 rebounds in a 140–136 win over the Minnesota Timberwolves. He became the youngest 20-point scorer in franchise history. On October 29, Dončić posted 31 points and 8 rebounds in a 113–108 loss to the San Antonio Spurs, for his first 30-point game in the NBA. He recorded his first NBA double-double on November 19, with 15 points and 10 rebounds in a 98–88 loss to the Memphis Grizzlies. Dončić was named NBA Rookie of the Month in the Western Conference for November 2018. On December 8, Dončić scored 21 points in a 107–104 win over the Houston Rockets. After initial struggles, he produced a personal 11–0 run in the game's final minutes. On December 28, Dončić scored 34 points and became the youngest NBA player to make seven three-pointers in a game. He was named Western Conference Rookie of the Month for December 2018. On January 21, Dončić recorded his first NBA triple-double with 18 points, 11 rebounds and 10 assists in a 116–106 loss to the Milwaukee Bucks, which made him the second-youngest player in NBA history to accomplish the feat at 19 years and 327 days old, behind only Markelle Fultz. On January 27, Dončić scored a season-high 35 points and recorded his second NBA triple-double adding 12 rebounds and 10 assists in a 123–120 loss to the Toronto Raptors. He became the first teenager in NBA history with a 30-point triple-double and with multiple triple-doubles. Two days later, Dončić was named a confirmed participant for the World Team in the 2019Rising Stars Challenge. Despite being second in fan voting, behind only LeBron James, and ranked 8th in total voting score, Dončić wasn't selected for the Western Conference All-Stars in the 2019 NBA All-Star Game.
Dončić made his first triple-double of the season on October 25, 2019, posting 25 points, 10 rebounds, and 10 assists to help the Mavericks defeat the New Orleans Pelicans, 123–116. In two consecutive games, on November 1–3, he not only recorded two triple-doubles but matched a career-high 15 assists in both games. On November 8, Dončić scored a career-high 38 points and recorded his twelfth NBA triple-double by adding 14 rebounds and 10 assists during a 106–102 loss to the New York Knicks. Ten days later, in a 117–110 win over the San Antonio Spurs, Dončić recorded a career-high 42 points and his sixth triple-double of the season by adding 11 rebounds and 12 assists. He made NBA history in a 142–94 win over the Golden State Warriors on November 20 when he posted 35 points, 10 rebounds, and 11 assists; thus becoming the youngest player to have 35-point triple-doubles in succession, breaking Oscar Robertson's record, and only the fourth player to record it since the 1983–84 season, joining Michael Jordan, James Harden, and Russell Westbrook. In November, Dončić was named the NBA Western Conference Player of the Week for Week 5 (November 18–24), his first NBA Player of the Week award. On December 3, he won his first NBA Player of the Month award when he was named the NBA Western Conference Player of the Month for October and November; becoming the youngest Western Conference Player of the Month winner since the league began issuing the award by conference in the 2001–02 season. In December, he was also named Sports Illustrated 2019 Breakout of the Year. On December 8, 2019, Dončić surpassed the record for the most consecutive games with at least 20 points, 5 rebounds, and 5 assists since the ABA-NBA merger in 1976. Michael Jordan previously held the record with 18 straight games in 1989. Dončić made his tenth season triple-double on January 4, 2020, posting 39 points, 12 rebounds, and 10 assists in a 123–120 loss to the Charlotte Hornets.
During the 2019–20 season, Dončić was selected to his first NBA All-Star Game as a Western Conference starter. He became the youngest European player to start in an All-Star game. On March 4, Dončić recorded his 22nd career triple-double, passing Jason Kidd for the most in franchise history. He registered 30 points, 17 rebounds, and 10 assists in a 127–123 overtime victory over the New Orleans Pelicans. Dončić made his 15th season triple-double on July 31, posting 28 points, 13 rebounds, and 10 assists in a 153–149 overtime loss to the Houston Rockets. On August 4, Dončić recorded another triple-double with 34 points, 12 assists, and a career-high 20 rebounds in a 114–110 overtime win over the Sacramento Kings. With that, he became the youngest player to record 30+ points, 20+ rebounds, and 10 or more assists. On August 8, Dončić had a career-high 19 assists, which tied Lebron James for an NBA season-high, along with 36 points, 14 rebounds, and just 2 turnovers, in a 136–132 win against the Milwaukee Bucks; the game marked his 17th triple-double of the season, and clinched his spot as the youngest ever player to lead the NBA in triple-doubles. On August 15, he was selected to the NBA's All-Bubble First Team for his outstanding play in the NBA's eight seeding games, where he averaged 30.0 points, 10.1 rebounds, and 9.7 assists per game. Dončić was announced as one of the three finalists for the NBA Most Improved Player Award. On August 17, Dončić made his NBA Playoffs debut, where he scored 42 points (most ever in an NBA playoffs debut) in a 110–118 loss to the Los Angeles Clippers. On August 23, he became the youngest player in NBA postseason history with a 40-point triple-double, scoring 43 points in a 135–133 victory over the LA Clippers, while hitting the game-winner.
On September 22, 2016, Dončić announced that he would represent the senior men's Slovenian national team for the rest of his career. He had previously been linked with several other national teams, including Serbia and Spain. His national team roommate became Goran Dragić, who he met at age 7 and has been cited as his mentor and friend.
Dončić was a member of the Slovenian squad for EuroBasket 2017, where his country won its first gold medal after going undefeated (9–0) in the tournament. In Slovenia's 103–97 win over Latvia in the quarterfinals, he scored 27 points and grabbed 9 rebounds. He recorded 11 points, 12 rebounds, and 8 assists, in the 92–72 semi-final win over Spain. In the final, which Slovenia won by a score of 93–85 over Serbia, he had 8 points and 7 rebounds, before falling out of the game, due to an injury, in the game's third quarter. Dončić was also named to the competition's All-Tournament Team, joining teammate Goran Dragić, who was also voted the EuroBasket MVP.
"[Dončić is] incredible with the ball for a big guy. He's unbelievable in pick and roll play. His court vision is already unbelievable. I couldn't believe what I saw from a 19/20-year-old. He's a good shooter when he has time and I think he's going to be great for [the Dallas Mavericks] for a long, long time... I could shoot a little bit but I never had the court vision... the savviness that he brings to the game... He's going to pick defenses apart and it's going to be fun to watch."
Since his early years with Real Madrid, Dončić was tabbed as one of Europe's premier talents, with Spanish newspaper Marca giving him the nickname "El Niño Maravilla" (Wonder Boy). Entering the 2018 NBA draft, he was widely seen as one of the best and most accomplished European prospects of his generation.Slam magazine considered Dončić the "best international prospect ever," and sports website SB Nation called him "most accomplished NBA prospect in decades." An anonymous NBA veteran scouting executive said that his game was "leap years above anyone" in his draft class.
Dončić is versatile on the offensive end, displaying proficiency in shooting three-pointers, mid-range jump shots, floaters, and shots in the post. His basketball IQ, intangibles, and skills have been considered his primary assets, and he is seen as an elite facilitator, especially on the pick and roll. NBA and EuroLeague coach Ettore Messina called him "phenomenal, especially mentally" for his age. His lack of lateral quickness to stay in front of most NBA point guards and wings has been labeled as one of his main flaws as a player. Dallas Mavericks head coach Rick Carlisle refuted some of the worries regarding Dončić's athleticism, stating that "for a 19-year-old, he's got a really unusual combination of size, speed, and deceptive quickness." By his sophomore year, Luka’s ability to accelerate off a pick and blow by defenders to get to the basket is seen as one of his strengths.
Before his draft, basketball journalist and scout, Austin Green, compared Dončić to NBA players Paul Pierce and Joe Johnson. Dončić compared himself to Ben Simmons due to his versatility. In his second season, LA Clippers coach Doc Rivers, when asked about Dončić, stated that "there's a lot of people in him." He likened Dončić’s stepback 3-pointers to James Harden, his passing ability to Larry Bird and his court vision to LeBron James. NBA analyst, Kendrick Perkins, called him "baby LeBron" due to his overall skill and dominance on the court.