Born the second son of Charles Manningham of Surrey, Manningham began his career as a subaltern in the 39th Foot serving under his uncle, Sir Robert Boyd, at the Siege of Gibraltar. On the outbreak of the French Revolutionary Wars in 1793, he was appointed as Major to the light infantry battalion where he fought in the Caribbean. He became Lieutenant-Colonel of the 81st Foot and then adjutant-general in Santo Domingo, under the command of Lieutenant-General Forbes.