Born John St. Aubyn on 23 October 1829, his father was Sir Edward St. Aubyn, who in 1866 gained the title 1st Baronet St. Aubyn, of St. Michael’s Mount, Cornwall. John St. Aubyn succeeded his father in 1872 as the 2nd Baronet, and in 1887 was raised to the peerage as 1st Baron St. Levan.

Baron St. Levan died on 14 May 1908 at the age of 78.