Mills was born at Camelford House, Park Lane, London on 26 April 1830.

In 1865 he entered Parliament for Northallerton, a seat he held until 1866 when he was unseated due to bribery by his agents.

[citation needed] He succeeded his father in the baronetcy in 1872, inheriting Hillingdon Court.

[4] In 1853, Lord Hillingdon married Lady Louisa Isabella Lascelles, daughter of Henry Lascelles, 3rd Earl of Harewood and the former and Lady Louisa Thynne (a daughter of the 2nd Marquess of Bath).

[5] Together, they were the parents of: He died in April 1898, aged 67, and was succeeded in his titles by his eldest son Charles.