Niven was the head of the William Morris Agency in Europe, which he left for Columbia Pictures in 1970. His many clients included Robert Woods. He was managing director of Paramount Pictures England until 1975, when he turned his focus to film production.

Away from film, Niven invested in the restaurant Drones, in Pont Street, London in 1972, which he recommended that it be called after Bertie Wooster’s fictional club. At his request a picture of his father was positioned on the wall. The restaurant was later run by Marco Pierre White’s restaurant group White Star Group. The location changed under new owners and closed in 2007.

In 1976, he produced The Eagle Has Landed, and in 1979, he produced Escape to Athena, which starred his father. He was nominated for a Primetime Emmy Award in 1985 as Executive Producer of The Night They Saved Christmas which he co-wrote with James C. Maloney.

At a book launch by Jackie Collins in 1987, Niven was asked would if he would ever write a book about his life, to which he replied “But how can I when everything, everything, I have ever done, said or thought appears in Jackie’s novels.”‘There’s nothing left,’ he laments. ‘I don’t know why the headings on some of the chapters shouldn’t be, ‘I’d like to dedicate this to…’ ”

Niven was a regular on the 1990 edition of To Tell the Truth, which was hosted by Gordon Elliot making 14 appearances.

In 1994 Niven and his brother Jamie gave the Online Archive of California their father’s archive. In 2009 Michael Munn released a biography of his father, David Niven, by which Niven Jr. was horrified. Niven and his brother had been close to their father and they challenged many of the claims in the book.

Niven was married to actress and producer Barbara Niven from 1993 to their divorce in 1998. He had previously had a relationship with Natalie Wood during the 1960s. He married his second wife Beatrice Anne Reeve, daughter of Annette de la Renta in 2000, but divorced in 2005. In 2009 he sold his house on Sunset Boulevard for $5 million.

During the 1990s he was the chair emeritus of the Recording Artists, Actors and Athletes against Drunk Driving (R.A.D.D) group in Hollywood, and founder of the bicycle safety group See a Child, Save a Child. In 2002 he successfully campaigned for a Child Safety Day and Week which was accepted by the City of Los Angeles.