In 2007, Fensom joined the Canberra Raiders, playing for their Jersey Flegg Cup side.
In 2008, he captained the Raiders' in the inaugural National Youth Competition season, starting at lock in their Grand Final victory over the Brisbane Broncos.
He was named at lock in the Toyota Cup Team of the Year.

In Round 5 of the 2009 NRL season, Fensom made his NRL debut for the Raiders, coming off the bench in their 24-14 win over the Cronulla Sharks.
He made his only other appearance that season a week later.
In Round 4 of the 2010 NRL season, he scored his first NRL try, against the Wests Tigers.

In Round 11 of the 2011 NRL season, Fensom equaled Nathan Hindmarsh's world record for the most tackles made in a single rugby league game: when he made 75 tackles against the Canterbury-Bankstown Bulldogs.
He went on to make a club record 1135 tackles for the season, breaking the record previously held by Alan Tongue.

Fensom won consecutive Mal Meninga Medals for Raiders' Player of the Year in the 2011 and 2012 seasons, becoming the 6th player in history to receive the award two years in a row.
In 2011, Fensom received 24 votes, which was nine ahead of second-placed Dane Tilse with 15.
He was also the winner of the 2011 "Tradies" Raider of the Year award, which is voted on by The Canberra Times rugby league reporters.
Fensom finished with 25 points at the end of the 2012 season, five ahead of Reece Robinson.

Fensom is known for his extremely high work rate, particularly in regards to tackling.
 In the 2012 season, he averaged 43.3 tackles per game.
Fensom ended the 2013 season having played 20 games, averaging 100 metres and 44 tackles per game whilst also knocking on the door of New South Wales Origin selection.

In 2014, Fensom played 18 games in an injury interrupted season, once again averaging over 40 tackles a game.
In 2015, Fensom played all but one game for Canberra.

In 2016, Fensom broke his arm during the pre-season but managed to be fully fit for their Round 1 clash against the Penrith Panthers in which he received man of the match honours, scoring the match winning try as well as running for 135 metres and ending the game with 38 tackles.
Fensom lost his first grade spot midway through the 2016 season, playing just 14 games.
He spent the back end of the season playing for Canberra's Intrust Super Premiership side Mounties, playing in their Grand Final side.
In 2007, Fensom joined the Canberra Raiders, playing for their Jersey Flegg Cup side. In 2008, he captained the Raiders' in the inaugural National Youth Competition season, starting at lock in their Grand Final victory over the Brisbane Broncos. He was named at lock in the Toyota Cup Team of the Year.
In Round 5 of the 2009 NRL season, Fensom made his NRL debut for the Raiders, coming off the bench in their 24-14 win over the Cronulla Sharks. He made his only other appearance that season a week later. In Round 4 of the 2010 NRL season, he scored his first NRL try, against the Wests Tigers.
In Round 11 of the 2011 NRL season, Fensom equaled Nathan Hindmarsh's world record for the most tackles made in a single rugby league game: when he made 75 tackles against the Canterbury-Bankstown Bulldogs. He went on to make a club record 1135 tackles for the season, breaking the record previously held by Alan Tongue.
Fensom won consecutive Mal Meninga Medals for Raiders' Player of the Year in the 2011 and 2012 seasons, becoming the 6th player in history to receive the award two years in a row. In 2011, Fensom received 24 votes, which was nine ahead of second-placed Dane Tilse with 15. He was also the winner of the 2011 "Tradies" Raider of the Year award, which is voted on by The Canberra Times rugby league reporters. Fensom finished with 25 points at the end of the 2012 season, five ahead of Reece Robinson.
Fensom is known for his extremely high work rate, particularly in regards to tackling.  In the 2012 season, he averaged 43.3 tackles per game. Fensom ended the 2013 season having played 20 games, averaging 100 metres and 44 tackles per game whilst also knocking on the door of New South Wales Origin selection.
In 2014, Fensom played 18 games in an injury interrupted season, once again averaging over 40 tackles a game. In 2015, Fensom played all but one game for Canberra.
In 2016, Fensom broke his arm during the pre-season but managed to be fully fit for their Round 1 clash against the Penrith Panthers in which he received man of the match honours, scoring the match winning try as well as running for 135 metres and ending the game with 38 tackles. Fensom lost his first grade spot midway through the 2016 season, playing just 14 games. He spent the back end of the season playing for Canberra's Intrust Super Premiership side Mounties, playing in their Grand Final side.
Shaun Fensom