McIntosh had joined the Liberal Party in 1982, and had been active in local branches. In 1999 he was preselected as the Liberal candidate for Kew, a safe seat being vacated by sitting member Jan Wade. He was duly elected, and was appointed Shadow Parliamentary Secretary from Infrastructure in 2001. In 2002 he became Shadow Minister for Industrial Relations and Shadow Attorney-General. In 2006, McIntosh was moved to the portfolios of Police and Emergency Services, Corrections, and Manager of Opposition Business. In March 2009,he attracted attention for criticising the government for not releasing a weather briefing it had received predicting an "absolute extreme fire weather spike day" four days before the Black Saturday bushfires. According to a Sunday Herald Sun investigation, McIntosh achieved little voter recognition as a frontbencher. Six months out from the 2010 state election, not one of 50 voters surveyed could identify him as the Shadow Minister for Corrections. McIntosh claimed that assaults in Victoria have doubled since 1999 and has been instrumental in Coalition policy advocating abolishing suspended sentences, a policy which was later mirrored by the Labor government. He also helped to develop Coalition policy advocating 1600 extra police, which was later also adopted by the government. He has advocated greater freedom of information and transparency under the Brumby government. He alleged that a dirt unit exists inside the Department of Premier and Cabinet, after in 2006 a notebook, pushed under his office door and belonging to an advisor to the Premier, referred to an "index search" on Ted Baillieu's wife and three children. With the election of Ted Baillieu's government in 2010, McIntosh was made Minister for Corrections, Minister for Crime Prevention and Minister responsible for the establishment of an anti-corruption commission in the Baillieu Ministry. 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.
