Archibald Kennedy, 4th Marquess of Ailsa, DL, JP, FSRGS (22 May 1872 – 27 February 1943), styled Earl of Cassilis until 1938, was a Scottish peer, barrister and soldier.

Styled Earl of Cassilis from birth, he was born at Berkeley Square, London, the eldest son of Archibald Kennedy, 3rd Marquess of Ailsa, and the Honourable Evelyn, daughter of Charles Stuart, 12th Lord Blantyre.

[1] Lord Cassilis was appointed a captain in the 3rd (Militia) Battalion of the Royal Scots Fusiliers on 7 January 1900,[2] and served in the Second Boer War 1900–02, where he won two medals and five clasps.

[3] Following the end of hostilities in early June 1902, he left Cape Town on board the SS Wakool,[4] and arrived at Southampton the next month.

[1] Lord Ailsa married Frances Emily McTaggart-Stewart, daughter of Sir Mark MacTaggart-Stewart, 1st Baronet, on 20 April 1903.