MacDonald (sometimes spelt MacDonell) was the second son of Ranald MacDonald, Chief of Clanranald. When still young he was sent to France where he received a commission in the Royal-Ecossais Regiment of the French army. In 1745 he was sent by King Louis XV to assist Charles Edward Stuart in the Jacobite rising. MacDonald was wounded at the siege of Stirling Castle and imprisoned after the surrender of the Jacobite forces. As a French officer he was released from imprisonment and returned to France.