An established television and comedic actress, Siobhan Finneran made her acting debut in 1986 in the feature film Rita, Sue and Bob Too! She has appeared in a number of long-running British television series, including Coronation Street and Benidorm among others. She has also appeared in the Masterpiece production The Amazing Mrs. Pritchard.
Finneran is fiercely defensive of her Downton Abbey character, O'Brien. "I think she's great. I really love playing her, and I love all her little scheming bits and all her little funny bits. I think her snidey comments are hilarious. I love all that about her."