Brewers manager Craig Counsell announced the decision Monday after the Brewers beat the Dodgers 4-0 to take a 2-1 series lead.
"It's conversation with Derek Johnson, our pitching coach, with David [Stearns], our general manager, and we kind of laid out some scenarios, kind of going into today's game, what the possibilities were for tomorrow," Counsell said. "And if we got a good start and we're in good shape, Gio was always going to be the guy."
Before announcing a pitcher for Game 3, Counsell had already said Wade Miley would start on short rest for Game 5, facing Dodgers ace Clayton Kershaw.
Gonzalez went only two innings after starting in Milwaukee's Game 1 victory over Los Angeles. He gave up a home run to Manny Machado in the second inning before being replaced by Brandon Woodruff, who entered in the top of the third inning.
Miley, who could either clinch the series or put Milwaukee one win away from their first World Series appearance since 1982 on Wednesday, pitched 5⅔ scoreless innings in his second career playoff start on Sunday and had two hits in his first multihit game since 2014.
Gonzalez was 3-0 with a 2.13 ERA in five starts for the Brewers after being acquired in a deal with the Washington Nationals.