McGuinness was born in Buncrana, Co Donegal. He has written extensively for the Irish theatre, both original scripts and translations. His awards include the London Evening Standard Award for most promising playwright for Observe the Sons of Ulster in 1985, and a Tony Award for his 1997 adaptation of Ibsen's A Doll's House. He has published several volumes of poetry and wrote the screenplay for Pat O'Connor's 1998 film version of Friel's Dancing at Lughnasa. He is a writer-in-residence at UCD. He lives in Dublin.