Son of John Erskine (d. 1739), 3rd of Alva, and Catherine Sinclair. Married (1761) to Janet Wedderburn (or Wederburn), a sister of Alexander Wedderburn, 1st Earl of Rosslyn. John Erskine was a distant cousin of Andrew Erskine, and also - and slightly less distant - of James Boswell himself.
In 1747 he inherited the Baronetcy of Alva from his older brother Charles Erskine, who was killed at the battle of Val on July 2, 1747. In 1749 he was elected MP for Ayr, and from 1754 until his death for Anstruther. At the time of his death, he was even a Lt-Gen in the army, as well as Secretary to the Order of the Thistle.
- 1. Other biographical sources include Henry Erskine's entry in the Dictionary of National Biography.