[7] After the escalation of the Second Boer War in late 1899, Rundle was in January 1900 appointed to the command of the 8th Division of the South African Field Force, with the temporary and local rank of lieutenant general.

[8][9] The appointment was described as "the most remarkable instance of advancement to high military office which has occurred in the recent history of [the] Army" by a contemporary issue of The Times.

[10] He left Southampton in the SS Moor in March 1900 with the staff of the 8th division and 600 men of militia regiments,[11] and arrived in Cape Town the following month.

He served as commander until early March 1902, when he returned to the United Kingdom on board the SS Carisbrook Castle.

[3] Rundle was presented with the Freedom of the borough of Dover on 29 October 1902, while living there as General Officer Commanding South-Eastern district.