Fremantle served in the Second Anglo-Burmese War in 1852 and the New Zealand Wars in 1864. Then in 1861 he became commander in HMS Eclipse. He was promoted rear-admiral in 1885 and was made second-in-command of the Channel Squadron in 1886 and Commander-in-Chief, East Indies Station in 1888. Promoted to vice-admiral from 1890 he went on to be Commander-in-Chief, China Station in 1892 and Commander-in-Chief, Plymouth in 1896. He was promoted to admiral later that year and retired in June 1901.