Glen was born on 24 June 1961 in Edinburgh, Scotland. Glen has an older brother Hamish Glen who is the artistic director of the Belgrade Theatre, Coventry, and former artistic director of the Dundee Repertory Theatre. Glen was previously married to Susannah Harker from 1993 to 2004 and they have a son Finlay Glen born in 1994. He has been in a relationship with actress Charlotte Emmerson and they have two daughters together; Juliet Glen born 2012 and Mary Glen born 2007. Leaving the Royal Academy of Dramatic Art in 1985, having won the prestigious Bancroft Gold Medal, Iain immediately rose to prominence with his acclaimed performance as a charismatic gang leader in The Fear for Euston Films. Followed by his multi award winning tour de force as imprisoned Scottish poet Larry Winters in Silent Scream he was set for a rich and varied career. Few actors have managed to maintain a balance between stage and screen and achieved such success in both. Iain has been described as "The greatest Scottish theatre actor of his generation."