Dickson entered the Royal Military Academy in 1793, passing out as second lieutenant in the Royal Artillery in the following year. As a subaltern he saw service in Menorca in 1798 and at Malta in 1800. As a captain he took part in the unfortunate Montevideo Expedition of 1806–07, and in 1809 he accompanied Brigadier General Edward Howorth to Portugal where he served as brigade-major of the artillery.