McNaughton is one of several candidates vying for the party's top spot after Tim Hudak announced he will be stepping down as leader following the PC's election defeat.
"I'm supporting Monte McNaughton because he's a family man," Ford said in a statement.
"He's the conservative in the PC leadership race. He will help the little guy and defend the taxpayer."
"I'm excited to welcome Rob Ford to the campaign and I look forward to working with him in the weeks and months ahead," McNaughton said.
"Rob Ford understands how to win in Toronto and I couldn't imagine a better boost for my campaign in the GTA."
Brothers supporting different candidates
Rob's brother Doug Ford had contemplated a run at the Ontario PC leadership position.
But in November, he announced he would not seek the leadership of the Ontario PC party, instead, throwing his support behind Whitby-Oshawa MPP Christine Elliott instead.