McIntosh was born in Melbourne, Victoria, and raised in North Balwyn, attending Bellevue Primary School.

In 1999 he was preselected as the Liberal candidate for Kew, a safe seat being vacated by sitting member Jan Wade.

In 2006, after a notebook was pushed under his office door belonging to an advisor to the Premier, referring to an "index search" on Liberal leader Ted Baillieu's wife and three children, McIntosh alleged that a dirt unit existed inside the Department of Premier and Cabinet.

In the Napthine Ministry in 2013, McIntosh also took the portfolio of Gaming Regulation, and the anti-corruption commission title became "Minister responsible for IBAC".

On 16 April 2013, McInstosh resigned all of his ministerial positions with immediate effect, after admitting that he had leaked confidential information from the parliamentary Privileges Committee to a journalist.