St Aubyn was born in 1960 in London, the son of Roger Geoffrey St Aubyn (1906–1985), a surgeon, and his second wife, Lorna Mackintosh (1929–2005). 

On his father's side, he is a great-great grandson of Sir Edward St Aubyn, 1st Baronet, and a great-nephew of John St Aubyn, 1st Baron St Levan. On his mother's side, he is a grandson of Captain Alastair William Mackintosh of the Seaforth Highlanders,[citation needed] who was briefly married to Constance Talmadge 1926–1927) and Lela Emery (later Duchess of Talleyrand), daughter of the American businessman John Josiah Emery, Sr. He is a great-nephew of John J. Emery, Jr. and Audrey Emery,[citation needed] wife of Grand Duke Dmitri Pavlovich of Russia.

Novels

Never Mind. Picador USA. 1992. 

Bad News. Picador USA. 1992. 

Some Hope. Heinemann. 1994. 

On The Edge. Chatto & Windus. 1998. 

A Clue to the Exit. Chatto & Windus. 2000. 

Some Hope: A Trilogy. Grove Press, Open City Books. 2003. 

Mother's Milk. Grove Press, Open City Books. 2005. 

At Last. Farrar, Straus and Giroux. 2012. 

Lost for Words. Farrar, Straus and Giroux. 2014. 

Dunbar. Hogarth Press. 2017. 

Double Blind. Harvill Secker. 2021.