Major General Alexander Whitelaw Thorneycroft, CB (19 January 1859 – 4 November 1931) was a senior British Army officer during the Second Boer War.

[2] Expecting military hostilities, Thorneycroft was one of several officers sent to South Africa to raise volunteer units shortly before the Second Boer War broke out in October 1899.

He raised a corps of troopers, later known as the Thorneycroft's Mounted Infantry, which served in the early stages of the war, including in the campaign to relieve Ladysmith, which was under siege by troops from the Boer republics.

Thorneycroft received a brevet promotion to lieutenant colonel and was appointed a Companion of the Order of the Bath in the April 1901 South Africa Honours list (the award was dated 29 November 1900).

[5] After the end of the war in June 1902, Thorneycroft was among a number of officers who left Cape Town on the SS Kildonan Castle in late July, arriving in Southampton the following month.