Dublin born, Rebecca grew up by the sea in Sandycove. Daughter of Stephen and Veronica Jane O'Mara, sister of Jason and Stephen James.She attended Holy Child School, Killiney and later did a degree in Drama and Theatre at Trinity College Dublin. On graduating, she moved to London and worked in film production for some years.In 2004, she began her acting training at LAMDA. Since graduation, she has worked mainly in UK and Irish theatre.