He began his professional career with Northampton Saints in 1996; in 2007 he moved to France to represent Brive before returning to England two years later to join Sale Sharks.

He was selected for the Barbarians, appearing in the game wearing the socks of his first club, Northampton Old Scouts RFC.

[10] It was rumoured of a move to Harlequins RL with then chairman Ian Lenagan supposedly talking to Cohen over recent months, however nothing official was ever announced and he shortly afterwards signed for Brive.

"[16] In late December, Cohen picked up a knee injury during Sale's 54–21 defeat to Leicester that side-lined him for six to eight weeks.

In February 2000, Cohen made his England debut against Ireland in the inaugural Six Nations Championship, scoring two tries.

[20] In June 2001, he joined the Lions tour to Australia, and although he did not figure in the Tests series he did score twice in the midweek match against New South Wales Country Cockatoos at Coffs Harbour.

Cohen initially endured a difficult time after helping England lift the World Cup, admitting that he had lost his appetite for the game[24] and he did not feature in the 2005 Six Nations Championship.

He regained a place in the squad for the summer tour of South Africa and raised the prospects for the 2007 Rugby World Cup.

However, in May 2007 Cohen ruled himself out of both England's summer tour and the World Cup, stating that he wished to spend time with his pregnant wife.

[30][31] He has been involved in efforts to make rugby more accessible to the hard of hearing, especially young deaf players.

[32] During March 2011 High and Mighty, the big and tall menswear specialist, appointed Cohen as the new face of the brand for 2011.

[39] On 18 June 2013, he was named as one of the initial inductees to the National Gay and Lesbian Sports Hall of Fame newly established in Chicago, Illinois.

[40] In 2010, Cohen donated a signed jockstrap to support GMFA, a British charity addressing gay men's health issues, which was sold at auction at the Royal Vauxhall Tavern.

[41] He also featured on the front cover and in an interview section of GMFA's printed FS Magazine in November 2010.

In December 2023, Cohen participated in ITV’s The Real Full Monty to raise awareness of cancer.