Samuel Sebastian Wesley (14 August 1810 – 19 April 1876) was an English organist and composer.

Born in London, he was the eldest child in the composer Samuel Wesley's second family, which he formed with Sarah Suter having separated from his wife Charlotte. Samuel Sebastian was the grandson of Charles Wesley. His middle name derived from his father's lifelong admiration for the music of Bach.

After singing in the choir of the Chapel Royal as a boy, Samuel Sebastian embarked on a career as a musician, and was appointed organist at Hereford Cathedral in 1832. He moved to Exeter Cathedral three years later, and subsequently held appointments at Leeds Parish Church (from 1842), Winchester Cathedral (from 1849) and Gloucester Cathedral (1865-1876).

Famous in his lifetime as one of his country's leading organists and choirmasters, he composed almost exclusively for the Church of England, which continues to cherish his memory. His better-known anthems include Thou wilt keep him in perfect peace and Wash me throughly. He also wrote several rather late examples of verse anthems, which contrast unison and contrapuntal sections with smaller, more intimate passages for solo voice or voices. Blessed be the God and Father, The Wilderness and Ascribe unto the Lord are of considerable length, as is his Service in E. The popular short anthem Lead me, Lord is an extract from Praise the Lord, O my soul. Several of his compositions for solo organ have enduring value and continue to be played in recitals.

One notable feature of his career is his aversion to equal temperament, an aversion he kept for decades after this tuning method had been accepted on the Continent and even in most of England.