Vernon started his pro career at the Border Reivers until they disbanded in 2007. His contract was then move to Glasgow where he would breakthrough into the team playing mainly at No. 8 or openside flanker.
With the establishment of the "Killer B's" as the first choice back row at Glasgow, he left the Warriors in 2011 for Sale Sharks, signing a two-year deal with hopes for more gametime to develop his game and enhance his prospects for more caps with Scotland.[5]
At the end of 2013 he returned to Glasgow.[6] However, he struggled to tie down a regular starting place in the back row due to injuries form and also stiff competition within the squad. This led to an unusual conversion in position to centre[7] following discussions with Warriors head coach Gregor Townsend and Scotland coach Scott Johnson, who hope to more readily use his 6-foot, 5-inch frame and evident pace.
Vernon announced his retirement from rugby to finish at the end of the 2018–19 season on 12 March 2019.[8]