Southwell joined the Navy at the age of sixteen and travelled to Australia as midshipman, and later as Mate, aboard the Fleet flagship HMS Sirius. He remained in the newly established penal colony for three years, including one year as commander of the lookout station at Sydney's South Head. A series of letters from Southwell to his parents in England offer depictions of early colonial life and the first substantive interactions between Europeans and Australian Aborigines. The letters also reveal clashes between the colonial Governor, Captain Arthur Phillip, and his senior military officer Major Robert Ross, and Southwell's deep pessimism regarding the colony's economic and governmental prospects.
Southwell returned to England in 1791 and was promoted to lieutenant in 1794. He saw active service in the early stages of the French Revolutionary Wars but was wounded in action off the Portuguese coast and died in Lisbon Hospital on 21 August 1797.
Southwell's naval service began in May 1780 when he enlisted or was press-ganged as a Landsman aboard the 90-gun HMS Ocean, which was then serving as guard ship in Plymouth harbour and later as part of the Navy's Western Squadron off the coast of France. After six months, on 13 November 1780, he was promoted to ordinary seaman and transferred to HMS Monkey, a newly purchased 12-gun cutter under the command of Ocean's former first lieutenant James Glasford. A month later he saw his first active service when Monkey pursued and engaged with an 18-gun French privateer off Great Yarmouth.
- Bladen 1978, p.661
- Winfield 2007, p.19
- Winfield 2007, p. 331