He played college football at Texas A&M and holds the school's season receiving touchdown record with 13, set in 2014.

Reynolds was selected by the Los Angeles Rams in the fourth round of the 2017 NFL draft.

[4] As a freshman at Tyler Junior College in 2013, Reynolds accumulated a total of 782 yards on 44 catches and was named to the second-team all conference.

The 13 touchdowns set a Texas A&M Aggies season school record, breaking the mark of 12 previously held by Pro Bowler Mike Evans and Jeff Fuller.

[22] In the last game of his junior year, against Louisville on December 30, 2015, in the 2015 Music City Bowl, Reynolds recorded career highs in receptions (11) and receiving yards (177).

[24] Going into his senior season, Reynolds had the choice of entering the National Football League Draft or staying for his final year with Texas A&M.

[40] During Week 2 against the Washington Redskins, Reynolds made his NFL debut with a 28-yard pass reception on a successful fake punt from Johnny Hekker.

[42] Reynolds began the 2018 season as a backup, but after fellow wide receiver Cooper Kupp went down with a season-ending torn ACL, Reynolds had an increased role in the offense, starting eight total games, including the final six of the regular season.

[44][45] The Rams defeated the Dallas Cowboys by a score of 30–22 in the Divisional Round with Reynolds having a 19-yard reception.

[46] In the NFC Championship, Reynolds had four receptions for 74 yards as the Rams defeated the Saints on the road by a score of 26–23 in overtime.

His best performance came in London, where he caught three passes for 73 yards and his only touchdown of the season, a 31-yard score in the Rams' 24–10 win over the Cincinnati Bengals at Wembley Stadium as part of the NFL International Series.

[49] Reynolds set career single-season highs in receptions (52) and yardage (618) in 2020, starting 13 of 16 games for the Rams.

[52] For the remainder of the 2021 season, Reynolds played in seven games (starting in five) and finished with 29 receptions for 396 yards and two receiving touchdowns.

In a 30–12 win over the Arizona Cardinals in Week 15, Reynolds caught a season-high six receptions for 68 yards and a touchdown.

[55] During the 2023 regular season, Reynolds played in all 17 games, starting in 13, and caught 40 passes for 608 yards and five touchdowns.

[56] In the Lions' NFC Wild Card Round against the Los Angeles Rams, Reynolds matched his season highs for receptions (five) and yardage (80) to help Detroit prevail 24–23 over the team that had originally drafted him.

[60] On October 12, Reynolds was placed on injured reserve after suffering a hand injury in the Broncos' Week 5 victory over the Las Vegas Raiders.