Sims made his Brisbane Broncos début in the Round 1, 2008 clash against reigning wooden spooners, the Penrith Panthers, in a 48–12 win.
Later that year, an elimination semi-final against the Melbourne Storm, Sims started the match in the back-row.
The Broncos were leading at the time, but went on to lose the game in the final minute, after Sims dropped the ball with two minutes remaining in the match, which led to the match winning try by Greg Inglis.
Sims described it as "one of the low points" of his career.
Sims played almost 60 games for the club and was one of the club's highest paid players, he played in the back-row and in the front row during his time at the Broncos.

Shortly after the Broncos' semi-final exit, Sims was named in the Fiji squad for the 2008 Rugby League World Cup and was later confirmed for the final squad.
He had only visited Fiji once in his life—for a holiday—but qualified to play for the country because his mother was born there.
 He was Fiji's starting second-rower for all four of their matches; Fiji qualified for the tournament's semi-final for the first time.

Sims fell out of the Broncos' starting line-up early in the 2009 season, finding himself playing for the Norths Devils in the Queensland Cup.
He was recalled to the Broncos' first thirteen for the team's finals campaign, in which they fell one match short of qualifying for the Grand Final.
However, he only played nine NRL matches in the following season, and in August signed to play for the North Queensland Cowboys in 2011.
Sims made his Brisbane Broncos début in the Round 1, 2008 clash against reigning wooden spooners, the Penrith Panthers, in a 48–12 win. Later that year, an elimination semi-final against the Melbourne Storm, Sims started the match in the back-row. The Broncos were leading at the time, but went on to lose the game in the final minute, after Sims dropped the ball with two minutes remaining in the match, which led to the match winning try by Greg Inglis. Sims described it as "one of the low points" of his career. Sims played almost 60 games for the club and was one of the club's highest paid players, he played in the back-row and in the front row during his time at the Broncos.
Shortly after the Broncos' semi-final exit, Sims was named in the Fiji squad for the 2008 Rugby League World Cup and was later confirmed for the final squad. He had only visited Fiji once in his life—for a holiday—but qualified to play for the country because his mother was born there.  He was Fiji's starting second-rower for all four of their matches; Fiji qualified for the tournament's semi-final for the first time.
Sims fell out of the Broncos' starting line-up early in the 2009 season, finding himself playing for the Norths Devils in the Queensland Cup. He was recalled to the Broncos' first thirteen for the team's finals campaign, in which they fell one match short of qualifying for the Grand Final. However, he only played nine NRL matches in the following season, and in August signed to play for the North Queensland Cowboys in 2011.
Ashton Sims