Seagate Castle is a castle and fortified town house in North Ayrshire, in the town of Irvine, close to the River Irvine, Scotland. The castle was formerly a stronghold, a town house, and later a dower house of the Montgomery Clan. The castle overlooks the oldest street in Irvine, which was once the main route between the town and the old harbour at Seagatefoot, which by 1606, was useless and abandoned due to silting. The remains of the castle are protected as a scheduled ancient monument.

Irvine is a town and former royal burgh on the coast of the Firth of Clyde in North Ayrshire, Scotland. The 2011 Census recorded the town's population at 33,698 inhabitants, making it the largest settlement in North Ayrshire, and 22nd largest settlement in Scotland. Irvine was designated at the fifth and final Scottish new town in November 1966. Irvine is the administrative centre and the seat of the North Ayrshire Council administration which has its headquarters based at Cunninghame House. Irvine was the site of Scotland's 12th century military capital and former headquarters of the Lord High Constable of Scotland, Hugh de Morville. It also served as the capital of Cunninghame and was, at the time of David I, Robert II and Robert III, one of the earliest capitals of Scotland.