Walter Blackett Trevelyan (18 March 1821 – 10 October 1894) was an English first-class cricketer and barrister.

Trevelyan was born at Netherwitton Hall in Morpeth to Raleigh Trevelyan and Elizabeth Grey.^[1] He was educated at Harrow School and the Edinburgh Academy,^[2] before going up to Gonville and Caius College, Cambridge.^[3] While studying at Cambridge, he made his debut in first-class cricket for Cambridge University against Cambridge Town Club at Parker's Piece.^[4] He played first-class cricket for Cambridge University until 1843, making six appearances and gaining a cricket blue.^[4][3] He appeared for a Midland Counties cricket team in 1843, playing against the Marylebone Cricket Club (MCC) at Leicester.^[4]

He graduated from Gonville and Caius College with a law degree in 1844, with admission to the Inner Temple coming in November of that year.^[3] He appeared in further first-class matches for the MCC, playing twice in 1846 and once in 1851.^[4] Playing a total of ten first-class matches, Trevelyan scored 155 runs at an average of 9.11, with a high score of 44 not out.^[5] He was later admitted to the Middle Temple in April 1858 and was called to the bar later that same month.^[3] He served as a barrister on the Northern and North-Eastern Circuits until his death in October 1894 at Golders Green.^[3] He was survived by his wife, Helena Caroline Trevelyan, who he had married in 1849, with the couple having four children.^[1] His great-nephew, Ralph Spencer, also played first-class cricket.