Born in London, she is the daughter of the actor Corin Redgrave and his first wife, Deirdre Hamilton-Hill, a former fashion model. They divorced when Jemma was nine. She has a brother, Luke Redgrave, who is an assistant cameraman, and two half-brothers, Arden and Harvey Redgrave. Her mother died in 1997 and her father died in 2010.
She is the niece of actresses Vanessa Redgrave and Lynn Redgrave and cousin of Joely Richardson, Carlo Nero and Natasha Richardson.
Jemma Redgrave enrolled at the London Academy of Music and Dramatic Art at the age of 18.
After graduation, Redgrave landed acting roles in the 1988 stage production of Strindberg's Easter, in Lady Windermere's Fan in Belfast, Northern Ireland, as Emily in Thornton Wilder's Our Town, Irina in a 1990 revival of Anton Chekhov's The Three Sisters in London's West End with her aunts Vanessa Redgrave and Lynn Redgrave, in 1993 with Colin Firth in Alexander Griboyedov's Chatsky at the Almeida Theatre, London and in A Midsummer Night's Dream in 2001 at the Albery Theatre, London. In 2010, she appeared in New York's Public Theater in The Great Game: Afghanistan which featured seven hours of on-stage acting. Redgrave appeared in four of the twelve plays.
Jemma was supposed to play the role of Stephanie Abrahams in Duet for One, but had to withdraw due to reasons that have not been confirmed.
She has appeared in many roles on British television and is best known for her portrayals as Eve Granger in Cold Blood, Dr. Eleanor Bramwell in Bramwell, Eleanor in The Buddha of Suburbia, Francesca Rochester in Judge John Deed, and Dee Stanton in Like Father, Like Son. In 2007, she portrayed the indolent Lady Bertram in Mansfield Park and Sophie Wall in Waking the Dead. She appeared as Kate Stewart (formerly played by Beverley Cressman in the two videos Downtime and Dæmos Rising), the daughter of The Brigadier (Lethbridge-Stewart), in "The Power of Three" episode of Doctor Who in 2012 and reprised the role a year later in the 50th anniversary episode "The Day of the Doctor"; and as an aloof psychiatrist, complicit in torture, in Episode 3 of Season 6 of George Gently. Also in 2013 she appeared as Doctor Zoe Evans in the BBC One drama series Frankie. She returned to the role of Kate Stewart in the Doctor Who (series 8) finale "Death in Heaven", and in the 2015 episodes "The Magician's Apprentice", "The Zygon Invasion" and "The Zygon Inversion". In 2015, she joined the cast of BBC medical drama Holby City as army medic Major Berenice (Bernie) Wolfe. After appearing in 59 episodes, Redgrave left the show in August 2017. It has, however, been intimated by producers of the show that she may return at some point in the future.
Her film roles include Evie Wilcox in Howards End, Diana Markham in Dream Demon and Daisie in Lassie in 2005.
Jemma Redgrave married Tim Owen, a London barrister, in 1992. Redgrave gave birth to their first son, Gabriel, in 1994. They were separated from 1997 to October 1998. However, the couple reconciled and, in 2000, Redgrave gave birth to a second son, Alfie.
Redgrave is a celebrity supporter of the British Red Cross where she is particularly interested in working with refugees and diplomatic asylum seekers. She was an active member of the Don't Attack Iraq movement in 2002 and 2003.