The Irish captain was rated doubtful after sustaining the injury against Ulster last weekend.
O'Driscoll is a part of an unchanged line-up to face the Saints at the Millenium Stadium in Cardiff.
Hooker Richardt Strauss injured a hip in the Ulster game but he has also been passed fit for the decider.
Leinster skipper Leo Cullen, who lines up alongside Scotland's Nathan Hines at second row, is one of six Ireland internationals in a pack which includes Sean O'Brien, who has scored four tries in this year's competition.
O'Driscoll helped Leinster clinch an emotional final triumph over Leicester two years ago and he is hungry for more European success.
"It's a very different mentality now," he said. "By winning it a second time you copper-fasten the fact that you are a quality side."
O'Driscoll turned down an invitation to last month's royal wedding between Prince William and Kate Middleton to concentrate on his preparation for the semi-final against Toulouse.
"As big an honour as it was to be asked, the team ethos comes first," he said.
Leinster: I Nacewa; S Horgan, B O'Driscoll, G D'Arcy, L Fitzgerald; J Sexton, E Reddan; C Healy, R Strauss, M Ross, L Cullen (captain), N Hines, K McLaughlin, S O'Brien, J Heaslip.
Replacements: J Harris-Wright, H Van Der Merwe, S Wright, D Toner, S Jennings, I Boss, I Madigan, F McFadden.