Sir Walter Calverley Trevelyan was born in Newcastle upon Tyne to Sir John Trevelyan 5th Baronet and Maria Trevelyan nee Spencer Wilson. He was educated at Harrow and University College Oxford. After University Trevelyan pursued interests in geology and natural history, and became a supporter of phrenology and temperance.

In 1833 he married Pauline Jermyn, daughter of the Reverend Doctor George Bitton Jermyn, Vicar of Swaffham Priory, and Catherine Rowland. Pauline shared Trevelyan's interests in natural history, particularly botany, and the pair traveled extensively throughout Europe.

In 1846 Trevelyan succeeded to his title and the family estates of Nettlecombe and Wallington. He continued to pursue diverse interests, co-editing a volume on the Trevelyan Papers, becoming president of numerous societies including the Phonetic Society, the United Kingdom Alliance for the Suppression of the Liquor Traffic, and of the National Temperance Society. He frequently donated specimens and money to museums, libraries and learned societies.

Pauline became an important patron of the arts, maintaining a close friendship with John Ruskin until her death. Her fondness for the Pre-Raphaelite movement is reflected in refurbishments made at Wallington Hall, in particular the Great Hall. She died in 1866 during a visit to Switzerland, accompanied by Trevelyan and Ruskin.

In 1867 Trevelyan married Laura Capel, daughter of Capel Lofft, lawyer of Troston Hall.

Trevelyan died at Wallington in 1879.