The Canadian and MMA fan-favorite, who's currently the UFC Welterweight Champion, is the first MAA fighter signed by the local clothing company.
It's Under Armour's first venture into the growing world of Mixed Martial Arts.
St. Pierre, sometimes described as the Michael Jordan of MMA, will begin appearing in ads later this year.
The fighter joins the likes of Ray Lewis, the Cubs' Alfonso Soriano and U.S. Olympic Snowboarder Lindsey Jacobellis, who are all endorse Under Armour.
