 He matriculated at Christ Church, Oxford on 19 January 1703, aged 15.Trelawny was an aide-de-camp to the Duke of Marlborough during the War of the Spanish Succession and took part in the Battle of Ramillies in 1706.He was returned as Member of Parliament for East Looe on the family interest at the 1708 British general election, probably with the support of his Tory uncles Bishop Trelawny, Bishop of Winchester and Major-General Charles Trelawny.