Harty was born in Northern Ireland, the fourth of ten children. His father was a church organist. He learned to play the viola, piano, and organ. When he was twelve he was organist at Magheracoll Church, County Antrim. He also had organist jobs at Belfast and Dublin. In 1900 he went to London where he was soon known as a composer and an excellent piano accompanist. In 1904 he married the singer Agnes Nicholls. For her he wrote a piece for soprano and orchestra called "Ode to a Nightingale".