Born in Sydney, New South Wales, Reynolds played his early football with St Peters JRLFC Alexandria Rovers, La Perouse United and Kensington United in the South Sydney Juniors competition and attended Matraville Sports High School. Reynolds played for the New South Wales under 17's team in 2007. When asked about his inspirations he responded that Andrew Johns, Matthew Johns and Darren Lockyer were his favourite players when he was a kid and that Nathan Merritt is his favourite South Sydney player of all time. He then added when asked "who is the most inspirational player or person on your career and how have they positively affected your football?", he responded "My brother – he's always on my back telling me to do extras and pushing me to be the best I can be." Reynolds graduated to the Rabbitohs' under-20s team 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. In the 2011 pre-season he suffered a season-ending ACL injury to his left knee.
After the highly publicised departure of Chris Sandow, Reynolds joined the Rabbitohs NRL squad in 2012. In Round 1 of the 2012 NRL season, Reynolds made his NRL debut for the South Sydney Rabbitohs against the Sydney Roosters at halfback, kicking 4 goals in the Rabbitohs 24–20 last minute loss at ANZ Stadium. In Round 11 against the St George Illawarra Dragons, Reynolds scored his first NRL career try and also kicked a field goal to win the match for the Rabbitohs 19–18 in golden-point extra time at WIN Stadium. On 16 August 2012, Reynolds re-signed with the Rabbitohs on a 3-year contract to the end of the 2015 season. At the end of season 2012 Dally M Awards he was named the NRL's rookie of the year. Reynolds also finished the season as the NRL's highest goal scorer with 97. Reynolds was also crowned the John Sattler Rookie of the Year and Members Choice Player of the Year at the South Sydney Red and Green Ball in 2012, amongst other awards. Reynolds played in all of the Rabbitohs 27 matches, scored 3 tries, kicked over 97 goals and kicked 2 field goals in an impressive debut year in the National Rugby League in the 2012 season.
On 27 January 2015, Reynolds extended his contract on a two-year deal, estimated $500,000 per season. On 23 January 2015, Reynolds was named in the South Sydney Rabbitohs tournament-winning 2015 NRL Auckland Nines squad. Reynolds was named the Player of the Tournament. In Round 5 against the Canterbury-Bankstown Bulldogs, Reynolds suffered a knee injury that could have seen him sidelined for up to 6–8 weeks after Bulldogs prop and captain James Graham ran into him to charge down a field goal attempt in the dying minutes. The Rabbitohs were awarded a penalty and team-mate Bryson Goodwin kicked the penalty goal to win the match for the Rabbitohs 18–17 at ANZ Stadium. Reynolds returned early, in Round 9 against the St George Illawarra Dragons, and helped the Rabbitohs 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. Reynolds again made an early comeback from injury in Round 14 against the Wests Tigers in the Rabbitohs 34–6 loss at ANZ Stadium. Reynolds finished the 2015 NRL season as the Rabbitohs highest point scorer with him scoring 1 try, kicking 53 goals and kicking 1 field in 18 matches. 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. 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.