Sir Frederick Milner was born in November 1849, the second son of the fifth baronet, William Mordaunt Edward Milner. Milner was educated at Eton and Christchurch College at Oxford University. He became the Conservative MP for York in 1883 defeating by a small margin Frank Lockwood, but lost the seat back to Lockwood in 1885.
In 1880 Milner married Adeline Gertrude Denison, the daughter of William Beckett-Denison, the MP who he had followed as the MP for Bassetlaw.
Sir Frederick Milner was the Conservative MP for York from 1883 to 1885 and for Bassetlaw from 1890 to 1906, having in 1904 being appointed at a Privy Councillor. After leaving Parliament due to increasing deafness, he was interested in the welfare of disabled soldiers, and spent much time to further their interests.
Milner died at the age of 81 in June 1931, and was succeeded in his baronetcy by his only son, William Frederick Victor Mordaunt Milner. A school, the Sir Frederick Milner secondary modern school in Retford, Nottinghamshire was named after him.