Fiennes was born in Ipswich, Suffolk, England, the son of Mark Fiennes (1933-2004), a farmer and photographer, and Jennifer Lash (1938-1993), a writer. He is a third cousin of the adventurer Sir Ranulph Fiennes. The eldest of six children, his siblings are actor Joseph Fiennes (Shakespeare in Love, Luther), Martha Fiennes, a director (in her film Onegin, he acted the title role), Magnus Fiennes, a composer, Sophie Fiennes, a filmmaker, Jacob Fiennes, a conservationist, and his foster brother Michael Emery, an archaeologist.

Fiennes trained at the Royal Academy of Dramatic Art and then joined the Royal Shakespeare Company in 1988. He is the only actor ever to have won a Tony Award for playing Hamlet on Broadway. In 2001, Fiennes received the William Shakespeare Award from the Shakespeare Theatre in Washington, D.C. Fiennes made his film debut in 1992 as Heathcliff in Wuthering Heights opposite Juliette Binoche, for which he received substantial acclaim and praise throughout Europe.

1993 was the "breakout year" for him. He had a major role in the very controversial Peter Greenaway film The Baby of Mâcon with Julia Ormond. Though the film was poorly received, Fiennes's career suffered no lasting consequences, and later that year he became known internationally for portraying the amoral Nazi concentration camp commandant Amon Goeth in Steven Spielberg's Schindler's List. For this he was nominated for the Academy Award for Best Supporting Actor. He did not win the Oscar, but did win the Best Supporting Actor BAFTA Award for the role. His portrayal as Göth also earned him a spot on the American Film Institute's Top 50 of movie villains.

In 1994, he portrayed American academic Charles Van Doren in Quiz Show, and in 1996 was nominated for the Academy Award for Best Actor for the World War II epic romance The English Patient. Fiennes' work has ranged from thrillers (Red Dragon) to animated Biblical epic (The Prince of Egypt) to campy nostalgia (The Avengers) to romantic comedy (Maid in Manhattan) and offbeat dramedy (Oscar and Lucinda).

Fiennes was cast as Lord Voldemort in the 2005 fantasy film Harry Potter and the Goblet of Fire and has retained this role for both the 5th film Harry Potter and the Order of the Phoenix and the 6th film Harry Potter and the Half-Blood Prince.

The Constant Gardener was released in 2005 with Fiennes as the title role. The film is set in the slums of Kibera and Loiyangalani, Kenya. The situation affected the crew to the extent that they set up the Constant Gardener Trust in order to provide basic education around these villages. Fiennes is a patron of the charity. His recent performance in the play Faith Healer gained him a nomination for a 2006 Tony Award.