He was the son of Patrick Chamberlain of County Louth, and Letitia (Lettice) Brownlow, eldest daughter of Sir William Brownlow (1591–1661), a High Sheriff of Armagh and his wife Eleanor O'Doherty (or O'Dougherty), daughter of the Irish rebel leader, Sir Cahir O'Doherty.
He took his grandfather's family name as a condition of inheriting his estate.
[1] Like his grandfather, Brownlow was appointed High Sheriff of Armagh for 1668 and 1669, and represented County Armagh in the Irish House of Commons between 1689 and 1711.
[2] Brownlow was one of only six Protestant members to sit in the short-lived Patriot Parliament called by James II of England in 1689; he was cleared of any wrongdoing during the Irish Parliament of 1692.
They had at least seven children, including William Brownlow, who like his father was MP for Armagh, and a daughter Lettice who married Robert Cope, MP and High Sheriff of Armagh.