Seth was born on 20 June 1952 in Calcutta. His father, Prem Nath Seth, was an executive of Bata Shoes and his mother, Leila Seth, a barrister by training, became the first female judge of the Delhi High Court and first woman to become Chief Justice of a state High Court in India.

Seth has published eight books of poetry and three novels. In 1980, he wrote Mappings, his first book of poetry. The publication of A Suitable Boy, a 1,349-page novel, propelled Seth into the public limelight. It was adapted into a BBC television drama miniseries in 2020. His second novel is An Equal Music deals with the troubled love-life of a violinist. Seth’s work Two Lives published in 2005 is a memoir of the marriage of his great-uncle and aunt.

In addition to The Golden Gate, Seth has written other works of poetry including Mappings (1980), The Humble Administrator’s Garden (1985), All You Who Sleep Tonight (1990) and Three Chinese Poets (1992). His children’s book, Beastly Tales from Here and There (1992) consists of 10 stories about animals. He has written a travel book, From Heaven Lake: Travels through Sinkiang and Tibet (1983), an account of a journey through Tibet, China and Nepal. He was also commissioned by the English National Opera to write a libretto based on the Greek legend of Arion and the Dolphin. The opera was performed for the first time in June 1994.

Seth was made a Commander of the Order of the British Empire in 2001.

Seth divides his time between the United Kingdom, where he bought and renovated the former home of the Anglican poet George Herbert near Salisbury, and India, where he has a family home in Noida, Uttar Pradesh. In 2006, he became a leader of the campaign against Section 377 of the Indian Penal Code, a law against sodomy.

A sequel to A Suitable Boy, A Suitable Girl, was announced in 2009.