In 1376, half of Knapdale, which included the castle, passed into the possession of John MacDonald I, Lord of the Isles, by a grant from his father-in-law, Robert II, King of Scotland.

[6] The 16th century manuscript known as The Book of the Dean of Lismore includes the lament of Aithbhreac Inghean Coirceadal (f. 1460), which remains a highly important poem in Scottish Gaelic literature.

Aithbhreac, after being widowed, composed a lament addressed to the rosary of her late husband, a Tacksman of Clan MacNeil and former constable of Castle Sween.

[8] A 2018 report from Historic Environment Scotland noted that Castle Sween is at "very high risk" of coastal erosion due to climate change.

[9] Castle Sween was featured in the 2021 Starz TV series Men in Kilts: A Roadtrip With Sam and Graham (from Outlander) episode 7 "Clans and Tartans".