McDonald was first active in politics at Edinburgh University where he was President of the Student's Representative Council and President of the University's LiberalAssociation. He was Liberal candidate for the Edinburgh East division at the 1929 General Election. Edinburgh East had been a Liberal seat until it was lost to Labour in 1924. In that badelection for the party, his predecessor finished third. McDonald was able to overtake the Unionist candidate but unable to defeat the sitting Labour MP. He did not stand for Parliament again.