 He was the uncle of John MacNider, the pioneering 2nd Seigneur of Grand-Métis and Métis-sur-Mer.Born at Paisley in Scotland, he was a younger son of William MacNider (b.1660), of Balsarock (or Balsarach), Ayrshire.The MacNiders had held several small estates in Ayrshire since the early seventeenth century, but spurred by the conflicts between Britain and France during the eighteenth century, Mathew and his brother William (father of John MacNider and Mrs James Johnston) moved into the import-export business.