An ensemble member of the Steppenwolf Theatre Company since 1979.
Graham Chase, Irwin's character on "My So-Called Life" (1994), was ranked #49 in TV Guide's list of the "50 Greatest TV Dads of All Time" [20 June 2004 issue].
He was awarded the 1982 Joseph Jefferson Award for Actor in a Supporting Role for "The Glass Menagerie", at the Northlight Theatre in Chicago, Illinois.
He was nominated for a 1998 Joseph Jefferson Award for Actor in a Principal Role in a Play for "Space" at the Steppenwolf Theatre Company in Chicago, Illinois.
He was nominated for a 2001 Joseph Jefferson Award for Actor in a Supporting Role in a Play for "Hedda Gabler", at the Steppenwolf Theatre Company in Chicago, Illinois.
He was nominated for a 2010 Joseph Jefferson Award for Actor in a Supporting Role in a Play for "A Parallelogram", at the Steppenwolf Theatre Company in Chicago, Illinois.