Stephen Grenville Fremantle (1810-18 April 1860) was a naval officer in the Royal Navy. He was the youngest son of Vice-Admiral Sir Thomas Fremantle. His brothers were Thomas, Charles and William. In 1823 he attended the Royal Naval Academy, Portsmouth, and then in 1828 served as midshipman on HMS Challenger followed by . In 1829 was promoted to lieutenant then, in 1836, to commander on HMS Clio, Southampton and HMS Wanderer at the Cape of Good Hope and on the South America Station and in China respectively.