Fellowes won the Academy Award for Best Original Screenplay for the murder mystery film Gosford Park (2001).

[1] His father was a diplomat and Arabist who campaigned to have Haile Selassie, Emperor of Ethiopia, restored to his throne during World War II.

Fellowes has three older brothers: Nicholas Peregrine James, actor; writer David Andrew; and playwright Roderick Oliver.

[4] The siblings' childhood home was at Wetherby Place, South Kensington,[5] and afterwards at Chiddingly, East Sussex, where Fellowes lived from August 1959 until November 1988, and where his parents are buried.

The house in Chiddingly, which had been owned by the whodunit writer C. H. B. Kitchin, was within easy reach of London where his father, who had been a diplomat, worked as an executive for Shell.

He has appeared in several West End productions, including Samuel Taylor's A Touch of Spring, Alan Ayckbourn's Joking Apart and a revival of Noël Coward's Present Laughter.

He believed that his breakthrough had come when he was considered to replace Hervé Villechaize as the assistant on the television series Fantasy Island, but the role went to actor Christopher Hewett instead.

[12] He was unable to get an audition for the Disney film Baby: Secret of the Lost Legend (1985) in Los Angeles, but was offered the role when he was visiting England.

[13] After this, Fellowes decided to move back to England to further his career, and soon played a leading role in the 1987 TV series Knights of God as Brother Hugo, the "ambitious and ruthless second-in-command" of a futuristic military cult.

Subsequently, in 1991 he played Neville Marsham in Danny Boyle's For the Greater Good and Dr. Jobling in the 1994 BBC adaptation of Martin Chuzzlewit.

He appeared as the leader of the Hullabaloos in the television adaptation of Arthur Ransome's Coot Club, called Swallows and Amazons Forever!

As a writer, he penned the script to the West End musical Mary Poppins (2006), produced by Sir Cameron Mackintosh and Disney, which opened on Broadway in December 2006.

His greatest commercial success was The Tourist, which grossed US$278 million worldwide, and for which he co-wrote the screenplay with Christopher McQuarrie and Florian Henckel von Donnersmarck.

[17] The series starred a large ensemble cast which included Hugh Bonneville, Michelle Dockery, Dan Stevens, Elizabeth McGovern, Jim Carter, Penelope Wilton, and Maggie Smith.

[14] In 2013 he wrote the screenplay for the romance drama Romeo & Juliet starring Hailee Steinfeld, Damian Lewis, and Paul Giamatti, which was adapted from the William Shakespeare play of the same name.

[19] In April 2016, a period novel, Belgravia, began being released in 11 weekly episodes, and is available, via an app, in audio and text format.

[23] Fellowes suggested that a younger version of Maggie Smith's Dowager Countess character from his Downton Abbey drama might appear in the new series, saying: "Robert Crawley would be in his early teens, Cora would be a child.

"[23] As the title suggests, the series would be set during the time of America's so-called Gilded Age – the industrial boom era in the United States in the late 19th and early 20th centuries – and portray the upper echelons of New York's high society during that period.

As reported in RadioTimes: "NBC's The Gilded Age is set to start shooting later this year, Fellowes tells RadioTimes.com.

[26]In August 2016, Fellowes indicated that his plans for The Gilded Age would not overlap substantially with the characters in Downton Abbey since most of them would have been children in those earlier "prequel" decades.

Writing for Creative Screenwriting, Sam Roads asked Fellowes, "Will there be any connection between The Gilded Age and Downton Abbey?"

[30] A report in early September 2018 stated that Fellowes had two projects underway, both in development: the Netflix series The English Game and The Gilded Age for NBC.

On 19 May 2022, Fellowes was awarded The Saint Nicholas Society of the City of New York, Washington Irving Medal for Literary Excellence.

Fellowes sits on the Appeal Council for the National Memorial Arboretum and is a Patron of Moviola, an initiative aimed at facilitating rural cinema screenings in the West Country.

[41][42][43] Fellowes publicly expressed his dissatisfaction that the proposals to change the rules of royal succession were not extended to hereditary peerages, which had they been would have allowed his wife to succeed her uncle as Countess Kitchener in her own right.

On 9 May 2012, Queen Elizabeth II issued a royal warrant of precedence granting Lady Fellowes the same rank and style as the daughter of an earl, as would have been due to her if her late father had survived his brother and therefore succeeded to the earldom.