Sir Joseph Barnby (12 August 1838 – 28 January 1896) was an English musical composer and conductor.
Barnby was born at York, as a son of Thomas Barnby, who was an organist. Joseph was a chorister at York Minster from the age of seven, was educated at the Royal Academy of Music under Cipriani Potter and Charles Lucas, and was appointed in 1862 organist of St Andrew's, Wells Street, London, where he raised the services to a high degree of excellence.
He was conductor of "Barnby's Choir" from 1864, and in 1871 was appointed, in succession to Charles Gounod, conductor of the Royal Albert Hall Choral Society, a post he held till his death. In 1875 he was precentor and director of music at Eton College, and in 1892 became principal of the Guildhall School of Music, receiving the honour of knighthood in July of that year. His works include an oratorio Rebekah, The Lord is King (Psalm 97), many services and anthems, and 246 hymn tunes (published in 1897 in one volume), as well as some partsongs and songs (among them the popular lullaby using Alfred, Lord Tennyson's words Sweet and Low) and some pieces for the pipe organ.