Born a son of Thomas Fremantle, 1st Baron Cottesloe and Louisa Elizabeth Nugent, daughter of Sir George Nugent, 1st Baronet and a descendant, through Louisa"s mother Maria Skinner, of the Schuyler family and Van Cortlandt family of British North America.
Fremantle joined the Royal Navy in 1849. He served in the Second Anglo-Burmese War in 1852 and the New Zealand land wars in 1864. Then in 1861 he became Commander in HMS Eclipse.
Promoted to Captain in 1867, he commanded HMS Barracouta, HMS Doris, HMS Lord Warden and HMS Invincible.
He was made Senior Naval Officer in Gibraltar in 1881 and then went on to command HMS Dreadnought. 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.
Fremantle was granted the honorary office of Rear-Admiral of the United Kingdom in July 1901, and kept this until 1926.
He was described as "the Father of the British Navy" in Time Magazine.
