His usual position is as a number 8. Sowerby also captained the Sharks in South Africa for a year in 2003 which was their 2nd worst finish in Super Rugby history. He also played for the South African national team, Springboks, making his debut against Samoa. He has also won the French championship in the 2007–08 season with his club Toulouse. In 2010, he won the Heineken Cup, also with Toulouse. He moved to FC Grenoble for the start of the 2012–13 season.
At the start of 2014, Sowerby announced his intention to retire from the game at the end of the 2013–14 season. He was subsequently appointed as the forwards coach of South African provincial side the Eastern Province Kings.
On 30 December 2014, Sowerby joining the backroom staff as the new forwards coach for French club Montpellier.