Kingston was born and raised in Epsom, Surrey, on the outskirts of London, the eldest of three daughters of a butcher and his German wife. Her mother's younger brother is actor Walter Renneisen. She was inspired to pursue acting by one of her teachers at the all-girls grammar school, Rosebery School for Girls. She later completed a two-year program at the Royal Academy of Dramatic Arts and went on to join the prestigious Royal Shakespeare Company.

Career

Kingston has appeared in a number of British produced television dramas, including Grange Hill, Crocodile Shoes, Moll Flanders and The Knock. She has also guest starred on The Bill. In 1997, Kingston gained American television fame after being cast on the medical drama ER at the start of the fourth season. Her character Elizabeth Corday was a British surgeon fellow arriving from England. This role she played for just over seven seasons until leaving in 2004, four episodes into Season 11.

Her film credits include The Cook, the Thief, His Wife & Her Lover (1989), A Pin for the Butterfly (1994), Croupier (1998), and Boudica (Warrior Queen in the USA) (2003) in which she played Boudica. In 2006, she starred opposite Christian Slater in the West End (London, England) production of One Flew Over the Cuckoo's Nest, playing Nurse Ratched to Slater's Randle Patrick McMurphy (characters famously portrayed by Louise Fletcher and Jack Nicholson in the 1975 film of the same name).

In 2006, Kingston claimed she was turned down for a role on ABC's Desperate Housewives for being too curvy. In the same article, she admits to considering and nearly attempting suicide after her split with ex-husband Ralph Fiennes.

On May 31 and June 7, 2008 she guest starred in the fourth series of the long running science fiction television programme Doctor Who in the two-part story "Silence in the Library"/"Forest of the Dead" as Professor River Song.

On 30 June 2008 it was announced that Alex will be playing the lead character, Ellie in new BBC One drama series, Hope Springs.