The Micklethwaites were the descendants of Dr. Joseph Micklethwaite of York, who had retired from his physician's practice and had purchased the manor of Swine, becoming a gentleman farmer and an active county magistrate.
Dr. Micklethwaite was married to Ann Topham, the widow of Christopher Topham, member of Parliament and York merchant, and the daughter of Percival Levett, a Sheriff of York and a merchant.
Joseph's elder brother was Thomas Micklethwaite of Swine, Yorkshire, who represented Arundel in Parliament, was later a Lord of the Treasury, and subsequently was named Lieutenant-General of the Ordnance.
[2] On 14 August 1724, he was created Baron Micklethwaite, of Portarlington,[3] in the Peerage of Ireland.
Lord Micklethwaite represented the town of Kingston upon Hull, in his native Yorkshire from 1727 to 1734.