 As the 1957 federal election approached, the Progressive Conservative party recruited McDonald as their candidate in the Hamilton South riding.On election day, 10 June 1957, a 25-year-old McDonald defeated Liberal party incumbent Russell Reinke as part of an Ontario sweep by the Tories, helping John Diefenbaker win a minority government.After winning two more terms in the 1958 and 1962 federal elections, McDonald was defeated by William Dean Howe of the New Democratic Party in the 1963 election.