Declan is a graduate of the Neighborhood Playhouse School of the Theatre in New York City. He moved to New York to study acting after graduating from Rockhurst College in Kansas City, Missouri, which he attended on a soccer scholarship.

He made his Broadway debut in Stones In His Pockets as stand-by to the Tony-nominated Conleth Hill. He also appeared on Broadway in 2008 as understudy to David Morse in the Tony-nominated production of Conor McPherson’s The Seafarer.

Off-Broadway credits include: Trust at the Kirk theatre; Paddywack at the Mint Theatre and Macalla Theatre Company; Pigtown, The Colleen Bawn (Drama Desk nomination), The Playboy of the Western World and The Shadow of a Gunman, all at the Irish Repertory Theatre.

Declan appeared in the film Sunburn with Cillian Murphy and appeared in an episode of the NBC series Kings, starring Ian McShane.