Tamsin was born in 1967 in Camden, London, the middle child. Her mother's family were of Polish-Jewish stock, and her father's were Scottish.
She attended the University of Birmingham and graduated with a Drama and Theatre Arts Degree. Shortly after, she joined long-running BBC Radio soap, The Archers in 1991, and remains with the show as of 2008.
She moved into TV comedy, working in Channel 4 hits, Black Books and Green Wing.
She has been married to actor Richard Leaf since 1997, and they have three children.