Combating youth employment and reforming taxation will be his priorities, he says.
"There is no time to lose,” Hollande said in his home base of Tulle, south-west France. “It is urgent. There comes a point where there must be ideas and the embodiment of change."
Party members will vote in October to choose the party’s candidate.
Other possible contenders include International Monetary Fund chief Dominique Strauss-Kahn, and current party leader Martine Aubry.
"It is an exceptionally difficult time for our country. The left must be up to the challenge. Otherwise we must fear the worst: extremism, defiance, resignation," Hollande said on Thursday. "It must raise hope and write a new page in our history."