In 2007, Reynolds was part of the team from Matraville Sports High School that won the NRL Schoolboy Cup 32–10 against Patrician Brothers' College Blacktown.

[5] Reynolds graduated to the Rabbitohs' Under-20s team in 2009 and in the 2010 Toyota Cup season he was one of the leading lights in the South Sydney side that went to the Grand Final.

[citation needed] After the highly publicised departure of Chris Sandow, Reynolds joined the South Sydney NRL squad in 2012.

With the likes of team-mates John Sutton, Issac Luke, Greg Inglis and Nathan Merritt he was able to guide the Souths to a second place ladder finish at the end of the regular season.

[20] Reynolds returned early, in Round 9 against the St. George Illawarra Dragons, and helped South Sydney to a 16–10 win at ANZ Stadium, snapping his team's three match losing streak, However he suffered a thumb injury that could have see him out for up to 8 weeks.

[21] Reynolds again made an early comeback from injury in Round 14 against the Wests Tigers in South Sydney's 34–6 loss at ANZ Stadium.

On 26 September 2015, Reynolds played for the Prime Minister's XIII against Papua New Guinea at halfback and kicked 2 goals in the 40–12 win at Port Moresby.

[23][24] On 11 December 2015, Reynolds and Souths officials dismissed rumours that he wanted a release from the club to join the Gold Coast Titans with departed 2014 premiership winning team-mate Chris McQueen.

Reynolds played in the second game of the 2016 State of Origin series as Queensland defeated New South Wales 26–16 at Suncorp Stadium.

Reynolds was ruled out of the final game in the series due to injury and was replaced by James Tedesco who made his origin debut at fullback, shifting Matt Moylan to five eighth.

Reynolds was later cleared of any damage but was overlooked for origin selection with NSW coach Brad Fittler opting to pick Nathan Cleary at halfback.

[36][37] In round 17 against Manly-Warringah, Reynolds kicked a field goal in the dying minutes as South Sydney won 21–20 at ANZ Stadium breaking a four-game losing streak.

Reynolds spoke to the media saying "I grew up across the road from Redfern Oval in apartments on Elizabeth Street and always wanted to play for Souths, so to have the chance to captain the team is amazing".

[51] In round 16, Reynolds broke Eric Simms record at South Sydney for most goals kicked in the club's 38–22 victory over Wests Tigers.

Reynolds then attempted a two-point field goal with one minute remaining but the ball fell short of the crossbar and Penrith held on to claim their third premiership.

[57] In Round 9 of the 2022 NRL season, Reynolds played against his former club for the first time and led Brisbane to a 32–12 victory over South Sydney at Stadium Australia.

[60] In round 11, Reynolds was medicabbed off the field in the opening 20 minutes of Brisbane's match against Melbourne after he hit his head on the ground which knocked him unconscious.

[61] In round 24, Reynolds became the second player in Australian rugby league history to kick 1000 goals during Brisbane's 54–10 victory over Parramatta at The Gabba.

Reynolds played in Brisbane's 26–24 loss against Penrith in the 2023 NRL Grand Final where he made a couple of key errors during the game including kicking the ball out on the full from a dropout on two occasions.

[63] On 12 February, a video emerged of Reynolds and teammate Patrick Carrigan being involved in a melee after the Brisbane club's annual fan day with one of the onlookers saying "let go of him... Adam... Pat... stop".

[64] Ahead of Brisbane's round 3 grand final rematch against Penrith, Reynolds was ruled out for an indefinite period with a knee injury.