Fielding's father, George, was an Anglican vicar at Hexham and his mother, Katherine Fielding Barnsley, was a descendant of the novelist Henry Fielding. His pen name was derived from his illustrious ancestor.

He earned a B.A. from Trinity College, Dublin in 1939, with prizes in anatomy and biology. He graduated M.R.C.S., L.R.C.P. from St. George's Hospital, London in 1943. He was a captain in the Royal Army Medical Corps in World War II. His medical practice included general practice in Kent and part-time practice at Her Majesty's Prison, Maidstone, from 1952 to 1964. He once said, "Medicine, to me, was a sentence I had to fulfill in order to be free to write...."

His first book, The Frog Prince and Other Poems, was published in 1952 in England.

In 1966 he moved to the United States, where he was author-in-residence at Washington State University in Pullman, Washington. He also became a full professor of English literature there, retiring in 1981 as professor emeritus. In 1964 he was awarded the W.H. Smith Award for The Birthday King, and for "the most outstanding contribution to English Literature over a two-year period" (1962—1963). In 1964 he was awarded the Gold Medal of the St. Thomas More Association for The Birthday King. In 1967 the degree of Doctor of Literature was conferred on him by Gonzaga University, Spokane, Washington.

He published eight novels, three books of poetry, and numerous short stories. Three of the novels chronicle the unsuccessful love affairs of the same protagonist, John Blaydon (In the Time of Greenbloom, Through Streets Broad and Narrow and Brotherly Love), "in a series of brilliant word pictures, evocative, authentic, macabre or hilariously funny."

He was married to Edwina Eleanora Cook and had five children. Michael,Jonathan, Mario Simon, Felicity and Mary Gabriel He died in Washington State in 1986 of lung cancer.

Poetry

• The Frog Prince and Other Poems (1952)
• 28 Poems (1955)

Fiction

• Brotherly Love (1954) (ISBN 9997512162)
• In the Time of Greenbloom (1956) (ISBN 978-0226248455)
• Eight Days (1958)
• Through Streets Broad and Narrow (1960) (ISBN 0226248445)
• The Birthday King (1962) (ISBN 0451024400)
• Gentlemen in Their Season (1966)
• New Queens for Old - A Novella and Nine Stories (1972) (ISBN 0688000541)
• Pretty Doll Houses (1979) (ISBN 0091367107)
• The Women of Guinea Lane (1986) (ISBN 0091639808)