MacMillan served in the Prince Edward Island legislature from 2000–2003, as part of Pat Binns's Progressive Conservative Party of Prince Edward Island government.
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He has been acknowledged by Lawrence MacAulay, former Solicitor General of Canada, and Pat Binns, former premier of Prince Edward Island and Ralph Klein, former premier of Alberta for his many contributions in promoting projects and business.
He was a New Democratic Party candidate in the 1978 provincial election and finished third against future premier Pat Binns.