[1] He succeeded his father as third Earl Fitzwilliam in the Peerage of Ireland on 28 August 1728.
[2] He was elected Member of Parliament for Peterborough on 4 May 1741,[3] and sat until he was created Baron Fitzwilliam in the Peerage of Great Britain on 19 April 1742.
He was made a Member of the Irish Privy Council on 6 June 1746,[4] and further created Earl Fitzwilliam in the Peerage of Great Britain on 6 September 1746.
[2] On 22 June 1744 at St George's, Hanover Square, Fitzwilliam married Lady Anne Watson-Wentworth, daughter of the Earl of Malton.
Lord Malton was later created Marquess of Rockingham; Lady Anne's brother was the future Prime Minister Charles Watson-Wentworth.