Michael Dennis Nahan (born 2 July 1950) 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.

Nahan was born in Ann Arbor, Michigan in 1950 as one of 13 children and grew up on a small farm, later graduating with a bachelor's degree in economics from Western Michigan University. After arriving in Australia in the late 1970s, he received a doctorate in economics from the Australian National University having previously completed a master's degree in agricultural economics.^[1][2]

Nahan arrived in Western Australia in July 1982. He joined the Western Australian Public Service before moving to the Institute of Public Affairs, a libertarian think tank, as a policy director. Between 1995 and 2005 he was Executive Director of the IPA.^[3]

Nahan entered politics at the 2008 Western Australian state election when he defeated incumbent Labor MP Tony McRae for the seat of Riverton in southern Perth.

Nahan served as the Trustee of the Parliamentary Superannuation Board and was Chairman of the Economics and Industry Standing Committee in State Parliament from November 2008 to August 2012.^[2][4] As part of the Economics and Industry Standing Committee, Mike Nahan presided over the Kimberley Ultramarathon Inquiry, an Inquiry set up to understand why five individuals received extensive burns. It was later determined that the fire was caused by an out of control prescribed burn being conducted by FESA, El Questro, the WA Police and the James Gino Salerno family, a cult residing around Kununurra.

After the Liberal/National government was reelected at the 2013 Western Australian state election, Nahan was promoted to cabinet as Minister for Energy, Finance, and Citizenship and Multicultural Interests by Premier Colin Barnett.^[4]

In 2018, Nahan revealed a substantial disputed liability, believed to be potentially hundreds of thousands of dollars, to the United States Internal Revenue Service. Despite being a member of the Western Australian Legislative Assembly since September 2008 and Treasurer in the Barnett Government for three years, this possible liability was only disclosed in 2018 during a debate over eligibility of dual citizens.^[17]

During the debate, Nahan stated that he no longer held a U.S. passport but was unable to renounce his American citizenship until the debt was resolved. The issue arose in 2010 when the IRS changed the way in which it calculated liability from Australian superannuation recipients. Nahan is reported to be one many thousands of U.S. citizens caught up in the changes and is awaiting the outcome of several court cases in the United States where lawyers are confident that, if successful, his liability will be expunged.^[18][19] For Liberal Party colleagues the issue raised further concerns about his ability to lead the decimated party in parliament to the 2021 Western Australian state election.^[20]