St-Pierre became by far the UFC's largest drawing card with his combination of good looks, pleasant personality and dominant fight skills.
He had hinted for several months, however, that he would walk away from the game which made him rich and famous.
That talk intensified following his November 16 victory over Johny Hendricks at the MGM Grand Garden in Las Vegas in the main event of UFC 167.
St-Pierre took a beating in that fight and his face was covered with welts and bruises from the force of the many powerful blows that Hendricks landed.
But St-Pierre said his health is fine, but that he has felt the pressure of 22 bouts and 15 title fights in the UFC.
UFC boss Dana White added at the conference call that Johny Hendricks will fight Robbie Lawler for the vacant title on March 15 in Dallas.