The second of three sons of Admiral Sir Hyde Parker and Anne Parker (née Boteler), Parker joined the Royal Navy in February 1796. After initial training at the Royal Naval Academy at Portsmouth he joined the fifth-rate HMS "Cambrian". He transferred to the fifth-rate HMS "Narcissus" in 1801, and having been promoted to lieutenant on 24 September 1804, took part in the capture of the Cape of Good Hope in January 1806 during the Napoleonic Wars. He transferred to the frigate HMS "Volontaire" later that year and, having been promoted to commander on 22 January 1806, took command of the sloop HMS "Prometheus" in March 1807 for the Copenhagen expedition.