Southwell, who has made 40 appearances in black and gold and has 59 caps for Scotland, has been forced to retire due to injury.
Injured during preseason, Southwell has been given medical advice to give up the sport after a long career that spanned three countries and four leagues, playing for Bristol, Worcester Warriors, Edinburgh, Stade Francais and London Wasps.
Southwell, an ever present figure in the Wasps team from when he signed for the Club in 2011, was awarded the Players’ Player of the Year after a fine and assured first year and was named Club Captain for the 2012/13 season.
Having won his first international cap for Scotland against Samoa in 2004, Southwell played in every match for his country until injury put an end to a 30-game run during the 2007 Six Nations. He went on to win another 29 caps, playing his last international fixture against Wales at Murrayfield in 2011.
On the news of his retirement, Southwell said “This has been a very difficult time for me and I am absolutely gutted that I have been forced to retire. It is a situation that I never thought I would find myself in and nothing quite prepares you for it. I believed I had so much more to give, which is why Terry Evans, our Physio, and I tried everything possible to get me fit after I sustained the injury in pre-season last year. I am extremely grateful for all his efforts along with the rest of the physio team.