Cooke was in practice as a barrister until his father died, in 1740. He had the life appointment as chief prothonotary, from 1732, and also inherited the family estate, Harefield in Middlesex.[1][2]
In 1742 Cooke entered parliament, as member for Tregony, supported by Hugh Boscawen, 2nd Viscount Falmouth.[4] At this stage, Horace Walpole called him "a pompous Jacobite". Leaving parliament in 1747, he was returned for Middlesex in 1750. Initially a Tory, he became a follower of William Pitt the elder in the later 1750s. In the 1760s he opposed the Stamp Act 1765. He was still the member for Middlesex when he died on 5 June 1768.[1]