Turned professional without any status prior to the second semester (would have been spring 2019) of his senior year at Alabama.

Teammates in his three and a half seasons at University of Alabama (2015-18) included PGA TOUR winner Lee Hodges (2016-18 -- two seasons), Robby Shelton (2015-16 season), Wilson Furr (2017-18 -- one and a half seasons), and Dru Love (2015-17 -- two seasons), son of 21-time PGA TOUR winner Davis Love III.

Introduced to golf by his parents at three years old and grew up on a Jerry Pate-designed course at Canebrake Country Club, where his family's home was along the ninth fairway, in Hattiesburg, Mississippi. Davis recalls, "I could walk 200 yards from my house and be on the driving range and putting green and clubhouse."

Shot a 58 at Canebrake in October 2013 when he was 16 years old. He was with five other friends after school one late afternoon, and on the last few holes, his friends - who played the first 12 holes, then stopped and watched him play the rest - shined lights on his ball for him to see; he had a 10-footer on the last to shoot 57 and left it on the front edge.

Previously shared an apartment in Dallas with fellow PGA TOUR winner Will Zalatoris as the two played the Korn Ferry Tour throughout the second half of 2019, 2020, and early 2021. The two became friends in the years following the 2014 U.S. Junior Amateur Championship, where Zalatoris defeated Riley in the championship match. At one point during the COVID-19 pandemic, the two built a "pseudo range" in their apartment, setting up a mattress and a net, and propping up a Trackman on pillows.

Played three and a half seasons at University of Alabama (2015-18), where he was a 2018 All-America Third Team selection and finished with a 71.30 career scoring average, which ranked No. 3 in program history behind Robby Shelton (70.42 from 2013-16) and Justin Thomas (70.73 from 2011-13). Earned his lone collegiate victory in September 2017 at the Olympia Fields/Fighting Illini Invitational, contested at Olympia Fields Country Club.

Alongside fellow PGA TOUR winner Lee Hodges, Riley helped Alabama to a runner-up finish at the 2018 NCAA Championship. The Crimson Tide were swept, 5-0, in the championship matches by an Oklahoma State team which featured future PGA TOUR winners Viktor Hovland, Austin Eckroat, and Matthew Wolff.

Played in consecutive U.S. Junior Amateur Championship title matches in 2013 and 2014. At the time, was the eighth player in history to play in multiple title matches, joining a group which included Tiger Woods (1991, 1992, 1993) and Jordan Spieth (2009, 2011). In 2013, led Scottie Scheffler 3 up, but eventually lost 3 and 2, with the match ending when Riley called a rules infraction on himself for nudging the ball at address prior to a long birdie putt from just off the green. In 2014, led Will Zalatoris 2 up, but eventually lost 5 and 3.

Runner-up finisher at the 2018 Western Amateur, where he defeated Min Woo Lee in the Round of 16, Hayden Springer in the quarterfinals, Tyler Strafaci in the semifinals. Fell to Cole Hammer in the championship match.

Quarterfinalist at the 2018 U.S. Amateur Championship, contested at Pebble Beach Golf Links. Also qualified for match play at the 2016 U.S. Amateur Championship, where he defeated PGA TOUR winner Matthew Wolff in the Round of 64 and lost to eventual champion Curtis Luck in the Round of 32. Previously qualified for match play at the 2015 U.S. Amateur Championship, contested at Olympia Fields Country Club.

Qualified for the 2015 U.S. Open as an 18-year-old high school graduate.

One of four recipients of the 2015 Byron Nelson International Junior Golf Award. One of the other three recipients that year was Sam Burns.

Represented the United States at the 2014 Junior Ryder Cup and 2018 Arnold Palmer Cup.