Son of James Somerville, 12th Lord of Somerville, and Janet Murray. Married (1724) to Anne Bayuntun (d. 1734) and (1736) to Frances Rotherham (d. 1755).
In 1726, Somerville commissioned the present house at The Drum on the outskirts of Edinburgh from architect William Adam.
Somerville was succeeded as Lord of Somerville by his son, a Major in the Dragoons and later a Representative Peer of Scotland, James (d. 1796).
Little is known about Boswell's connection with Lord Somerville. Early biographers, such as Charles Rogers in Boswelliana (1874), believed that they didn't meet until 1761, when Somerville invited Boswell to his table, following an account of London which Boswell had published in a local Edinburgh periodical.
Pottle, however, suggested that they met some years before that time. This interpretation is supported by certain references by Boswell to "Lord Somerville's kindness to me at a very early period" (James Boswell: The Earlier Years 1740-1769, p. 36), by the fact that Lord Somerville was a major personality in Edinburgh's theatrical community, and by the fact that some references in the 1759 pamphlet A View of the Edinburgh Theatre, which was probably written by Boswell. Some reviews in the pamphlet clearly referred to (and even paraphrased) reviews probably written by Lord Somerville in the early 1750s. Boswell and Somerville had a shared interest in theatre and poetry.