After purchasing a captaincy in 1784 he remained on half-pay until 1790 when he exchanged into the 40th Regiment of Foot and was promoted to brevet major in 1794. Kemmis took part in the Flanders Campaign until the army was evacuated from Bremen in April 1795. He sailed with his regiment to the West Indies where he was promoted to brevet lieutenant-colonel. After service on the Helder Expedition and the 1801 Egyptian Campaign he did not accompany the 40th to South America but remained in Ireland.