The son of James Cunningham, 7th Earl of Glencairn by his spouse Margaret (d. January 1610), daughter of Sir Colin Campbell of Glenorchy and Katherine Ruthven.
William succeeded his father in 1630 but enjoyed the earldom only for a short time, dying himself in October that year.
Finlaystone House and estate in Inverclyde was the seat of the Earl of Glencairn and chief of clan Cunningham from 1405 to 1796.
He married Janet Kerr, daughter of Mark Kerr, 1st Earl of Lothian, by his wife Margaret Maxwell, daughter of John Maxwell, Lord Herries of Terregles.
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