Aged fourteen, he entered the Glasgow University. In 1705 his nineteen-year-old brother died, making the eighteen-year-old John Cochrane 4th Earl of Dundonald. On 4 May 1706 he married Lady Anne Murray and they produced four children. However, four years later she died of smallpox.
At the election of Scottish Representative Peers on 17 June 1708, as he was a minor his votes were set aside. However, in 1713 and 1714 he was a Scottish Representative Peer. On 15 October 1715 he married Mary, Dowager Duchess of Beaufort, and daughter of the 2nd Duke of Leeds. From 1715 until 1719 he was Colonel of the 4th Horse Guards and died, 5 June 1720, aged nearly thirty-three.

Source: Leo van de Pas