Colton Underwood graduated from Illinois State University, where he followed his father's footsteps to play college football for the Redbirds.
On May 10, 2014, Underwood was signed as an undrafted free agent by the San Diego Chargers. On August 30, 2014, he was waived. On September 3, 2014, Underwood was signed to the Philadelphia Eagles' practice squad. On September 9, 2014, he was released from practice squad.
On September 23, 2014, Underwood returned to the Chargers and was signed to their practice squad. On December 29, 2014, he signed a future contract. On September 5, 2015, he was waived. On September 6, 2015, he was placed on injured reserve. On September 10, 2015, he was waived from injured reserve.
On December 1, 2015, Underwood was signed to the Oakland Raiders' practice squad. On August 29, 2016, he was released by the Raiders.
After getting eliminated in week 8 after hometown dates, Underwood was cast in season 5 of Bachelor in Paradise. After being linked to fellow contestant Tia Booth, Underwood broke it off, and both left Paradise separately in the fourth week.
On September 4, 2018, ABC announced that Underwood would star in the 23rd season of The Bachelor. The announcement received mixed reactions on social media. On September 21, 2018, ABC announced that Colton had started filming The Bachelor and had already met three of his contestants on The Ellen DeGeneres Show.
On April 14, 2021, Variety reported that Underwood was in production for his own unscripted series at Netflix.
In January 2016, Underwood founded the Colton Underwood Legacy Foundation to raise money for cystic fibrosis research and medical equipment. Underwood started the foundation after his cousin Harper was disagnosed with the disease. In January 2018, the foundation began the Legacy Project, with the goal of delivering AffloVests, chest wall oscillation devices which clear excess mucus from lung airways as part of the daily treatment for cystic fibrosis, to children in 50 US States.
From 2016 to 2017, Underwood dated gymnast Aly Raisman after he asked her out in a video.
Underwood has spoken publicly about his choice to remain a virgin, and how appearing on The Bachelorette helped him discuss the topic. He began dating speech pathology student Cassie Randolph after meeting on season 23 of The Bachelor. When Randolph initially ended their relationship during the final three, Underwood broke things off with the other two women and asked Randolph for a second chance without the pressure of an engagement. Underwood and Randolph were in a relationship from November 2018 until May 2020.
In September 2020, Randolph filed a restraining order against Underwood, alleging that he stalked her outside her Los Angeles apartment and her parents' Huntington Beach house, sent harassing text messages using an anonymous number, and installed a tracking device underneath her car. Randolph was granted a temporary restraining order against Underwood ahead of the October hearing.