Cain called Gingrich "a patriot" who's "not afraid of bold ideas."
Cain is set to campaign with Gingrich on Monday in an 11th hour push for support. The nod from the former pizza executive and tea party favorite could give a boost to Gingrich in Tuesday's Florida primary.
"I had it in my heart and mind a long time ago," Cain said.
Former Texas Gov. Rick Perry also endorsed Gingrich when he bowed out of the race in South Carolina.