He represents the electoral district of Inverness in the Nova Scotia House of Assembly as a member of the Progressive Conservative Party.

Prior to being elected, MacMaster worked as an investment advisor with BMO Nesbitt Burns, and authored a monthly column for the Nova Scotia Business Journal entitled "Building Your Wealth".

[9] Since 2013, he has been an advocate for patient safety and the access to a CT scanner at the Inverness hospital,[10] and a voice for those opposing the "Royal" designation of the Gaelic College in Cape Breton.

He was appointed Deputy Premier, Minister of Finance and Treasury Board, Gaelic Affairs and Labour Relations on August 31, 2021.

[15] On October 24, 2024, MacMaster resigned from cabinet and announced he is seeking the nomination for the Conservative Party of Canada in Cape Breton—Canso—Antigonish.