Brereton was born in 1789, and entered the Royal Military Academy as a "Gentleman Cadet" in 1803, passing out on 10 May 1805 as a second lieutenant in the Royal Artillery, and gaining promotion to first lieutenant on 7 June 1806. He served in the Peninsular and Waterloo campaigns from December 1809 to June 1815, including the defence of Cádiz, where he commanded the guns at Fort Matagorda, the battle of Barrosa, where he was wounded, the Burgos retreat, the battles of Vitoria and the Pyrenees, the siege of San Sebastián, where he was temporarily attached to the breaching batteries, the battles of Orthez, Toulouse, Quatre Bras, and Waterloo. During the greater part of the time, he was one of the subalterns of the famous "H Troop" of the Royal Horse Artillery commanded by Major W. Norman Ramsay, with which he was severely wounded at Waterloo. He became a second captain on 5 November 1816, and was placed on half-pay the year after. On 23 January 1819, while still on half-pay, he was promoted to major. He was brought on full pay again in 1823, and, performed further varied service at home and in the colonies. He was invested as a Knight of the Royal Guelphic Order in 1837 and as a Companion of the Order of the Bath in 1838. Brereton served as Inspector-General of the Irish Constabulary between 1839 and 1843, being promoted to lieutenant-colonel on 17 August 1843.