Sims played his junior football for the Gerringong Lions and Wests Panthers before being signed by the Brisbane Broncos, along with his brothers, Ashton and Tariq in 2008. Sims played for the Queensland U16's and U18's teams. He played for the Broncos NYC team in 2010, playing alongside his brother Tariq, scoring 2 tries in 9 games. In 2011, Sims joined the Newcastle Knights, playing in the NYC team in 2011 and 2012, scoring 14 tries in 40 games. In 2012, Sims was named at in the inaugural Under 20's State of Origin match for Queensland, but withdrew due to a broken hand. Sims was named at prop in the 2012 Toyota CupTeam of the Year. On 2 October 2012, Sims was named at in the Junior Kangaroos team to face the Junior Kiwis.
2013
In Round 3 of the 2013 NRL season, Sims made his NRL debut for the Knights against the North Queensland Cowboys off the interchange bench, playing against his brother Ashton in the Knights 34-6 win at Hunter Stadium. On 3 June, Sims re-signed with the Knights on a 2-year contract after rejecting offers from the Cowboys and Manly-Warringah Sea Eagles. Sims made 12 appearances for the season. He was selected in the Fiji 24-man squad along his brothers Ashton and Tariq for the 2013 Rugby League World Cup, playing in 3 matches and scoring a try in his Fiji international debut against Ireland in the 32-14 win at Spotland Stadium.
2014
In Round 7 against the Broncos, Sims scored his first NRL career try in the Knights 32-6 loss at Hunter Stadium. In May, Sims played for Fiji in the Pacific Rugby League International. Fiji lost the test match 32-16, but Korbin stole the limelight with a massive shot on Samoan opponent Isaac Liu. Sims finished the year with him playing in 20 matches and scoring 2 tries.
2015
In the pre-season, Sims played for the Knights in the 2015 NRL Auckland Nines. On 13 March, he again re-signed with the Knights on a 2-year contract. On 2 May, he played for Fiji against Papua New Guinea in the 2015 Melanesian Cup. On 10 May, Sims groped the genitals of opposition player and former teammate Willie Mason, an action described by Rugby League writer Brad Walter as being "infantile", "bizarre and offensive", and worthy of punishment due to the potential for the incident to portray the NRL in a distasteful and damaging light. Despite some rugby league reporters calling for harsh disciplinary action as a result of the incident, Mason was unperturbed, stating that he found the incident "hilarious." Sims received a warning from the NRL match review committee. Sims apologized for any offence caused to those who were watching the game and described it as a "harmless gesture between two friends." On 10 June, Sims was named as 20th-man for the Queensland team for game 2 of the 2015 State of Origin series. In the same match, his brother, Tariq, was named as 19th-man for New South Wales. However, neither of them played in the match. Sims finished off the 2015 season having played in 22 matches and scoring 2 tries.
2016
On 12 January, Sims was selected in the QAS Emerging Maroons squad. In February, he played for the Knights in the 2016 NRL Auckland Nines. He finished the 2016 season having played in 22 matches and scoring 3 tries. In October, he played for Fiji against Samoa, starting at lock in the 20-18 win at Apia Park.
2017
In January, Sims signed a 2-year contract with the Brisbane Broncos starting effective immediately, after being released from the final year of his Knights contract. He made his Broncos debut in round 1 of the 2017 season, starting at prop against the Cronulla-Sutherland Sharks, in the Broncos' 26-18 win at Shark Park. In round 6 against the Sydney Roosters, he scored his first try for the Broncos in their 32-8 win at Suncorp Stadium. On 6 May 2017, Sims played for Fiji against Tonga in the 2017 Pacific Cup, starting at lock in Fiji's 26-24 loss at Campbelltown Stadium. In Round 25 against the Parramatta Eels, Sims suffered a season ending arm injury in the Broncos 52-34 loss at Suncorp Stadium, later ruining his chances to play for Fiji in the 2017 Rugby League World Cup. Sims finished the 2017 NRL season with him playing in 22 matches and scoring 5 tries for the Broncos.
2018
In Round 2, in the Broncos Queensland derby match against the North Queensland Cowboys, Sims played his 100th NRL career match in the 24-20 win at Suncorp Stadium. On 18 July, Sims signed a three year deal to join the St George Illawarra Dragons starting in 2019. On 9 September, Sims endured a horror afternoon on the field against his future side St George as his brother Tariq ran past him on three occasions to score a hat trick in the dragons 48-18 victory in week one of the finals eliminating Brisbane from the competition.
2019
Sims made his debut for St George against his former club the Brisbane Broncos scoring a try in a 25-24 victory at Suncorp Stadium. The following week, Sims was taken from the field with what was later to be revealed as a broken arm. Sims had remained on the field for a further 15 minutes after breaking his arm despite being in obvious discomfort. Sims was later ruled out for 8 weeks. Sims made a total of 16 appearances for St George in the 2019 NRL season as the club suffered one of their worst ever seasons finishing in 15th place on the table.
2020
On 15 February, Sims suffered a broken arm whilst playing for St. George in the pre-season NRL Nines tournament against Parramatta. Sims was seen by cameras leaving the field in emotional distress.
