In round 7 of the 2012 NRL season, Sezer made his NRL debut for the Gold Coast Titans against the Manly-Warringah Sea Eagles at five-eighth and scored a try in the Titans 26-14 upset win at Brookvale Oval. In December 2012, Sezer re-signed with the Titans on a 2-year contract. Sezer finished his debut year in the NRL with him playing in 18 matches, scoring 4 tries, kicking 7 goals and kicking 1 field goal for the Gold Coast Titans in the 2012 NRL season. On 4 December 2012, Sezer re-signed with the Titans for three years until the end of the 2015 NRL season.
2013
On 9 February 2013, Sezer played for the Indigenous All Stars team in the 2013 All Stars match against the NRL All Stars off the interchange bench in the Indigenous Team 32-6 win at Suncorp Stadium. Sezer finished the 2013 NRL season with him playing in 22 matches, scoring 1 try, kicking 75 goals and kicking 2 field goals for the Gold Coast Titans.
2014
In round 10 against the Brisbane Broncos at Suncorp Stadium, Sezer suffered a pectoral muscle injury in the Titans 22-8 loss which made him miss 3 months of football, until making a return in Round 22 against the Sydney Roosters at SFS which the Titans lost the match 26-18. Sezer finished the Gold Coast Titans 2014 NRL season with him playing in 13 matches, scoring 4 matches, kicking 23 goals and kicking 1 field goal in an injury riddled year.
2015
On 20 January, Sezer was named in the Titans 2015 NRL Auckland Nines squad. On 10 April, he signed a 3-year contract with the Canberra Raiders starting in 2016. He finished his last year with the Titans, having played in 18 matches, scoring 3 tries, kicking 51 goals and 1 field goal.
2016
In round 1 of the 2016 NRL season, Sezer made his club debut for the Canberra Raiders against the Penrith Panthers, playing at halfback and scoring two tries in the club's 30-22 win at Canberra Stadium. On 8 May 2016, Sezer played for City Origin against Country Origin, where he played at five-eighth and kicked 6 goals in the 44-30 win in Tamworth. Sezer finished the 2016 NRL season with him playing in 24 matches, scoring 5 tries and kicking 5 goals in his first year with the Canberra club.
2017
In February 2017, Sezer was selected in Canberra's 2017 Auckland Nines squad. On 10 February 2017, Sezer played for the Indigenous All Stars against the World All Stars in the 2017 All Stars match, playing off the interchange bench in the 34-8 win at Hunter Stadium. In round 5 against the Parramatta Eels, Sezer played his 100th NRL career match in the 30-18 win at Canberra Stadium. Sezer finished the 2017 NRL season with him playing in all of the Raiders 24 matches, scoring 4 tries and kicking 12 goals. Sezer and his halves partner Blake Austin were subjected to criticism at the end of the season for not lifting their game to close out matches and were taking the back seat for hooker Josh Hodgson who did the key playmaking a little too often than they should have.
Sezer started the 2019 NRL season as the club's first choice halfback and kicked a field goal in the opening round as Canberra defeated the Gold Coast 21-0. In round 2, Sezer suffered an oblique injury and was replaced by Sam Williams. Due to the good form of Canberra and Williams, Sezer was kept in reserve grade to play for Canberra's feeder club side the Mount Pritchard Mounties after recovering from his injury. In round 23, Sezer played his 150th NRL game in Canberra's 14-18 loss to the Manly-Warringah Sea Eagles at GIO stadium in Canberra. In round 24, Sezer kicked 3 field goals in Canberra's 15-14 win against the Cronulla-Sutherland Sharks at Pointsbet Stadium, including the game winner in golden point extra time. Sezer played for Canberra in the 2019 NRL Grand Final which was their first decider in 25 years. Canberra would go on to lose the final 14-8 against the Sydney Roosters at ANZ Stadium. On November 28, it was announced that Sezer had signed a two-year deal to join Super League side Huddersfield.
