He was the brother of actor Sir Johnston Forbes-Robertson and a friend of Ellen Terry, Oscar Wilde, Edward Elgar and Henry Irving.

Together with Bram Stoker, he helped to organize Irving's funeral; a large body of letters connected with this event still exist.

[nb 1] He was educated at University College School, London and studied acting under Samuel Phelps.

His first stage appearance was on 20 November 1875 when he played Sir Harry Guildford in Shakespeare's King Henry VIII at the Gaiety Theatre.

[1] Forbes also had a career as an art dealer and in 1901 was credited with discovering the painting Christ in the House of Martha and Mary by Johannes Vermeer.