Family
- grandparents : Maternal grandparents; born and raised in India
- father David Firth: Born c. 1934 in India; travelled to various locations to teach; became history lecturer at King Alfred's College in Winchester, England
- mother Shirley Firth: Born c. 1936 in India; lecturer on comparative literature at Open University
- sister Kate Firth: Born in 1961
- brother Jonathan Firth: Born in 1967
- son William Firth: Born in 1990; mother, Meg Tilly
- son Luca Firth: Born in March 2001; mother, Livia Giuggioli
- son Mateo Firth: Born in August 2003; mother, Livia Giuggioli
- grandfather : Paternal grandfather; performed missionary work abroad
Companions
- Jennifer Ehle: born in December 1969; met during filming of "Pride and Prejudice"; no longer together
- Meg Tilly: met during filming of "Valmont"; together c. 1989-94; mother of Firth's son Will
