The decision was taken for "the urgent need at this time to dispel the uncertainties surrounding the appointment of a chief of general staff," Barak said.
The choice of Gantz has to be ratified by the government on Sunday and also by an ethics committee.
Barak's first choice for the post, Major General Yoav Galant, was ruled out by the attorney general and the state comptroller last Tuesday after he was accused of illegally obtaining land around his house on Moshav Amikam.
Galant commanded Israel's 22-day war on the Gaza Strip in December-January 2008, during which at least 1,400 Palestinians, more than half of them civilians were killed and thousands of others were displaced.
Former chief of staff Gabi Ashkenazi and Barak were "no longer able to work together," Netanyahu said.
Tension between the two increased amid calls by politicians and public figures to extend Ashkenazi's term as chief of staff beyond his scheduled retirement on February 14 and until the cabinet appoints a suitable successor.
Barak has formerly accused Ashkenazi of ethical and professional flaws.
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