[16] As a collegiate player, Richardson was stated to have displayed "dynamic talent" as a passer and runner during his college years but lacked accuracy and consistency.

[21] He joined Cam Newton and Daunte Culpepper as the only quarterbacks to have achieved a perfect RAS score.

[22][23] During his first training camp with the Colts, Richardson underwent nasal septum surgery to improve his breathing.

[24][25] On August 15, 2023, Richardson was named by head coach Shane Steichen as the Colts' starting quarterback over Gardner Minshew and Sam Ehlinger.

[31] On October 9, 2023, Richardson was placed on the injured reserve due to a grade three AC joint sprain he suffered in Week 5 against the Tennessee Titans, which was initially announced for him to miss one to two months.

[38] After two losses with Flacco, the Colts announced that Richardson would be the starter for the remainder of the season, beginning in their Week 11 matchup against the New York Jets.

[39] In his return as the starter, Richardson completed 67% of his passes for a career-high 272 yards, a touchdown, and added two rushing scores, including the game-winner in the final minute as the Colts won 28–27.

[40] In Week 13, Richardson orchestrated a 19-play, 80-yard touchdown drive, capped off with a go-ahead two-point conversion with under 15 seconds left as the Colts came back to win 25–24 over the New England Patriots.