Sir John Mitford was Speaker of the House of Commons between 1801 and 1802 and Lord Chancellor of Ireland between 1802 and 1806.

In 1877, he was created Earl of Redesdale, in the County of Northumberland, in the Peerage of the United Kingdom.

The Earl bequeathed his substantial estates to his first cousin twice removed, the diplomat, politician and writer Sir Bertram Mitford, the great-grandson of historian William Mitford, who was the elder brother of the first Baron Redesdale.

[3] He was succeeded by his second but eldest surviving son, David Freeman-Mitford, 2nd Baron Redesdale, who is chiefly remembered as the father of the famous Mitford sisters.

He died childless in 1962 when the title passed to his younger brother, the fourth Baron.