Sir Nicholas Slanning (1 September 1606 – July/August 1643) was an English soldier and politician who sat in the House of Commons from 1640 to 1642. He was a Royalist army officer active in the West of England, during the English Civil War.
Slanning was the son of Gamaliel Slanning of Hele, Devon, by his wife and cousin Margaret Marler, daughter of Edward Marler of Crayford, Kent. The Slanning family is first documented in 1538 and spanned nine generations until the extinction of the male line in 1700. It was granted or acquired land in Bickleigh, Walkhampton, Maybury, and Roborough, all near Plymouth.
In 1612 he inherited the Devonshire manors of Maristow, Walkhampton, and Bickleigh all near Plymouth. He attended Exeter College, Oxford and was admitted to the Inner Temple in 1628. However, he left the next year for the Low Countries "to learn the arts of war".
Slanning returned to England and was knighted on 24 August 1632 at Nonsuch Palace. He was appointed to the Commission for Piracy in Devon and Cornwall and as Vice-Admiral of the Southern Shores of both counties. He was subsequently appointed in 1635 Governor of Pendennis Castle, which castle guards the entrance to Falmouth harbour, in succession to William Killigrew (1606–1695). During this time he was resident at Trerose in the nearby parish of Mawnan.