Brodie was one of a collateral branch of the Brodies of Brodie, after serving for many years, both in the navy and mercantile marine, was promoted to the rank of lieutenant on 5 October 1736. In 1739 he served under Vernon at Porto Bello, and in 1741 at Cartagena. On 3 May 1743 he was made commander, and appointed to the sloop "Merlin" in the West Indies, and for about four years was repeatedly engaged with French and Spanish cruisers and privateers, several of which he captured and brought in. In one of these encounters he lost his right arm. Early in 1747 Rear-Admiral Knowles appointed him acting captain of ; but he was not confirmed in that rank until 9 March 1747–8, when, after the capture of Port Louis, he was appointed to .