Promoted to colonel, Kemmis took command of the 1st Battalion of the 40th, which arrived in Portugal on 1 August 1808 as part of Wellington's corps for service in the Peninsular War. He was mentioned in dispatches following the 1808 Battle of Vimeiro, and also fought at the battles of Roliça and Talavera for which he received the Army Gold Medal with one clasp.