He was the son of William St Clair, 15th Baron of Roslin and his wife Jean or Janet Edmondstone, daughter of the Laird Of that Ilk.

[2] William St Clair, 16th Baron of Roslin received a charter of the Hereditary Protectorate from the Scottish Freemasons in 1630.

[3] He objected to the appointment of Anthonie Alexander to be the Master of Work to the Crown of Scotland as being in prejudice to his hereditary charge of the Masons of the Kingdom.

[1] His tomb was excavated at the start of the 18th century and the findings recorded by a Father Hay and kept at the Advocates Library in Edinburgh.

This states the body was buried in full armour wearing a red velvet cap and resting on a stone slab, with no coffin, as were his ancestors.