Michael Dennis Nahan is a former Australian politician who was Leader of the Liberal Party of Australia's Western Australian branch and Leader of the Opposition from the 2017 state election until his resignation in June 2019. He served as Treasurer of Western Australia under the Barnett Ministry from March 2014 until the government's fall in March 2017. Nahan was also the Member of the Legislative Assembly for Riverton from 2008 until 2021, when he was succeeded by Labor's Jags Krishnan.

In the Australian state of Western Australia, the Leader of the Opposition is the leader of the largest minority political party or coalition of parties in the Legislative Assembly of the Parliament of Western Australia. By convention, the leader is generally a member of the Legislative Assembly.