W. J. Craig was born in Macosquin, County Londonderry, Ireland and was educated at Portora School, Enniskillen. In 1861 he was admitted to Trinity College, Dublin, graduating BA in 1865 and being awarded his MA in 1870. He remained at Trinity as a lecturer in literature and history until 1874 when he moved to London, where he became a private tutor for the Civil Service and Army entrance examinations, and university matriculation. From 1877 until 1879 he held the position of Professor of English at University College, Aberystwyth.
In 1901 he succeeded Edward Dowden, a friend from his student days at Trinity, as general editor of the Arden Shakespeare series, while continuing to teach English literature to private pupils from his rooms at 55a Gloucester Place, London.
Craig died in London on 12 December 1906.