Bloomfield was born in 1768, the son of John Bloomfield and Anne Charlotte Waller, and educated at the Royal Military Academy Woolwich. He was commissioned as a second lieutenant in the Royal Artillery in 1781. After seeing action at the Battle of Vinegar Hill in June 1798 during the Irish Rebellion, he served in Newfoundland, Gibraltar, and at Brighton in 1806, where, as a brevet major, he was in charge of a troop of the Royal Horse Artillery. He was also appointed a Gentleman in Waiting to the King that year. Promoted to major-general on 4 June 1814, he served as Member of Parliament (MP) for Plymouth from 1812 from 1818 and was made a Privy Councillor on 19 July 1817.