Shackleton was born in Bradford, the son of a paper manufacturer and merchant. He attended Bradford Grammar School and then studied art at Bradford Technical College. He won a Royal Exhibition to study at the Royal College of Art in 1893. He travelled to France and Italy on a British Institute Scholarship and spent a time in Paris where he studied at the Academie Julian. On his return to Britain he initialled settled in Sussex where he worked with his friend Edward Stott and the small artistic group that gathered around him in the South Downs village of Amberley. In 1905 he moved to Fulham, London where he shared a studios with Philip Connard and Oliver Onions, although he still spent his summers with Stott in Sussex. He exhibited at the Royal Academy, 1895-1919, the New English Art Club, 1901-33 and at many other venues. His first one-man show was held at the Goupil Gallery in 1910, a retrospective exhibition was held at the Leicester Galleries in 1922 and a memorial exhibition was held at Cartwright Hall, Bradford in 1933. Works by him are in the collection of the Tate Gallery, York, Bradford, Manchester and elsewhere.