Steuart was descended from another Sir James Stewart, knight, an Edinburgh merchant and staunch Presbyterian, who supported Charles II in the British Civil Wars of 1642-1660 and who died in 1681, having made enough money to purchase landed estates for his sons; three of those sons were prominent enough to have their families receive the title of Baronet after the Glorious Revolution of 1688. They were: Sir Thomas Steuart of Coltness, the first son; Sir James Steuart of Goodtrees, Lord Advocate, the fourth son; Sir Robert Steuart of Allandale, the youngest of the seven sons. The Lord Advocate, Sir James Steuart of Goodtrees, was his grandfather; his father, also Sir James Steuart, was the eldest son of the Lord Advocate, and rose to be Solicitor General for Scotland.