Williams has played 65 first grade matches for the Canberra Raiders and 4 for the St. George Illawarra Dragons. He has scored 12 first grade tries. Sam made his NRL début for the Canberra Raiders against the Cronulla-Sutherland Sharks in round 1 of the 2011 NRL season due to an injury sustained by then Canberra Raiders first choice halfback Matt Orford. Williams impressed on his début with a strong all round performance that earned him the man of the match award. In round 6 of the season Orford was again ruled out through injury, giving Williams another opportunity in first grade, in this game against the North Queensland Cowboys Williams was sent to the sin bin for a professional foul. Later in the season Williams managed to cement his spot as the first choice number of seven.
In July 2013, Williams signed a one-year contract with the St. George Illawarra Dragons starting in 2014.[4]
In June 2014, after only being selected for 4 games in 13 rounds for the St. George Illawarra Dragons, Williams joined the Catalans Dragons in the Super League on a 1-year contract effective immediately.[5]
He returned to the Canberra in 2015 on a two-year deal.[6]
In round 2 of the 2016 NRL season, Williams wore a special James Bond themed jersey with the number 007 on the back. He would kick the match winning field goal in that game with the Canberra club winning 21–20.[7]
Later in 2016, Sam rejected a new contract offer with the Canberra and signed a one-year contract with English Super League club Wakefield Trinity for the 2017 season,[8] after which he re-joined Canberra on a 2-year deal.[9]
In round 17 of the 2021 NRL season, he scored two tries for Canberra in a 30–16 victory over an Origin depleted Manly side.[14]
In round 15 of the 2022 NRL season, it was announced Williams would leave the Canberra Raiders having been unable to make it back into the top grade side. Williams played 8 games, scored 3 tries and kicked 15 goals for the Raiders NSW Cup side that year.
Post Playing
Williams retired from playing in 2022 and went on to become the Captain-Coach of the Queanbeyan Kangaroos Rugby League squad in the Canberra Raiders Cup.[15]