Leven began his career as a soldier on the continent, raising a regiment of Scottish refugees in Germany and Holland. A supporter of William of Orange, he crossed to Britain with his regiment in 1688 and the following year took part in the campaign against James VII and II's friend, Viscount Dundee. A contemporary described him as 'a man of good parts and sound judgement' although 'master of no kind of learning'. During the 1708 Rising, he treated his Jacobite prisoners at Edinburgh Castle with great civility. The artist, Medina, was brought to Scotland by Leven's father, the 1st Earl of Melville.