De Belin played part of his junior football career with St Gregory's College, Campbelltown and the Cootamundra Bulldogs in Group 9.

He was then signed by St George Illawarra and competed in the 2011 National Youth Competition where he made it into the team of the year squad.

[7] In 2014, de Belin signed a year extension deal with St George Illawarra which would see him play with the club until the end of 2017.

[11] In May 2017, de Belin was named in an extended New South Wales side to take on Queensland in Game 1 of the 2017 State of Origin series.

[14] On 13 December 2018, de Belin was charged by police with aggravated sexual assault following an encounter with a woman in Wollongong, New South Wales.

[20] On 13 February 2020, it was announced that De Belin's trial would be delayed until 8 April 2020 after a significant witness in the case became ill and was unable to attend court.

[22] Adams was also criticised for not separating the woman who had accompanied the alleged victim to the police station, even though he knew she would later become a key witness in the trial.

[28] In February 2020, de Belin sued newspaper, The Daily Telegraph for defamation over a front-page story published in 2019 that referenced the allegations.

[32] After nearly 1000 days since his last competitive match, de Belin played for St. George Illawarra's NSW Cup side against Western Suburbs on 29 May 2021.

[36] De Belin played 24 games for St. George Illawarra in the 2022 NRL season as the club finished 10th on the table and missed the finals.

[37] In round 17 of the 2023 NRL season, de Belin made his 200th first grade appearance in St. George Illawarra's 48-18 loss against the New Zealand Warriors.