Sinéad made her professional debut as an actor, working with the legendary Tomás macAnna of the Abbey Theatre. In 1990, she emigrated to the US, settling in New York City, where she began her career appearing in Hugh Leonard’s Da and The Country Boy both directed by the late Chris O’Neill for the Irish Bronx Theatre Company. Sinéad appeared off-Broadway in Sharon directed by the veteran stage and screen actress Geraldine Fitzgerald at the 91st Street Playhouse, Brian Friel’s Lovers Losers with Chris O’Neill at the Irish Arts Centre and Our Lady of Sligo, a joint production of the Irish Repertory Theatre and Out of Joint, London. During her years in New York City, Sinéad studied at the Herbert Berghof Studio, with William Hickey, Earle Hyman, Sandy Dennis and dialect coach Ruth Berkowitz.
Sinéad’s regional American theatre appearances include Dancing at Lughnasa at the Asolo Repertory Theatre in Sarasota, Florida and at Indiana Repertory Theatre, Indianapolis.
In 1997, Sinéad founded the theatre company Banba’s Crown with her husband Michael and four other New York based Irish actors. For Banba’s Crown she directed and performed in alternative adaptations of JM Synge’s Riders to the Sea and The Tinkers Wedding presented at the first New York International Fringe Festival. Also for Banba’s Crown Sinéad directed Samuel Beckett’s Catastrophe and Micheál macLiammóir’s The Importance of Being Oscar for the New York Irish Festival of the Arts in Soho, NYC. In 2012, she began working on a new adaptation of The Importance of Being Oscar and has directed her husband Michael in this highly acclaimed one man show.