[1][2] He was the son of John Bartlett Allen (1733–1792) a local landowner and colliery owner and his first wife Elizabeth Hensleigh.
He had 9 sisters, and his brothers-in-law included Josiah Wedgwood II, Sir James Mackintosh (both Whig MPs), John Wedgwood the horticulturist and Jean Charles Léonard de Sismondi the historian.
He was educated at Westminster School and Trinity College, Cambridge, following his elder brother Lancelot Baugh Allen.
He married Gertrude, daughter of Lord Robert Seymour, on 9 November 1812.
This article about a Member of the Parliament of the United Kingdom (since 1801), for a Welsh constituency is a stub.