"We never gave up hope that he would be present even this year,'' tournament director Zeljko Franulovic said. "Events proved us right and we are very proud.''
The second-ranked Federer is a three-time finalist at the clay-court tournament but has never won. Last year, top-ranked Rafael Nadal beat Federer 7-5, 7-5 in the final.
Nadal will be going for his fifth straight title at this year's tournament in Monaco, which will include nine of the world's top 10 players. Only sixth-ranked Andy Roddick will miss the event.
Red Bulls feeling pressure to perform
Federer accepts wild card for Monte Carlo Masters
