Richard Colley (as he was christened) was born around 1690, the son of Henry Colley (died 1719) and Mary, daughter of Sir William Ussher. He graduated from Trinity College, Dublin with a BA in 1711 and an MA in 1714 and an N.F.P. on 6 July 1740 as Richard Colley. In the intervening year he held the office of Chamberlain of the Court of Exchequer (Ireland).

On 23 September 1728 Colley inherited the estates of Dangan and Mornington, in County Meath, on the death of his cousin, Garret Wesley Less than two months later on 15 November 1728 he legally changed his surname to Wesley.

Between 1729 and 1746 Wesley represented Trim in the Irish House of Commons. He was High Sheriff of Meath in 1734 and he was created Baron Mornington in the Peerage of Ireland on 9 July 1746.

The Colley or Cowley family had come to Ireland from Glaston, in Rutland about 1500; Sir Henry Colley was elevated to the Peerage as Lord Glaston by Henry VIII. He married the daughter of Thomas Cusack, Lord Chancellor of Ireland, Catherine Wellesley Cusack (d. 1598) whose grandmother was a Wellesley. Upon the death of his cousin, Garret Wesley and his inheritance of the estates of Dangan and Mornington, Richard Colley (d. 1758) and his wife Elizabeth Sale (d. 17 June 1738) daughter of John Sale, Registrar of the Diocese of Dublin, on 23 December 1719. adopted the name Wellesley (from both Elizabeth's maternal family side from Catherine Wellesley Cusack, her grandmother) and through her husband's family, his cousin, Garret Wesley (Wellesley).