His father was prominent in Liberal Party politics in Leicestershire, and with his cousin Michael founded Millets Stores in 1928 in Leicester.
[5][6] Millett was educated at Harrow School, London, and at Trinity Hall, Cambridge, where he received a Master of Arts in Classics and Law in 1954, graduating with a Double First.
Between 1967 and 1973, Millett was junior counsel at the Department of Trade and Industry in chancery matters, and between 1971 and 1975 member of the General Council of the Bar.
He was a member of the Law Commission working party on co-ownership of the matrimonial home in 1972 and 1973 and appointed a Queen's Counsel in the following year.
On 1 October 1998, he was appointed a Lord of Appeal in Ordinary, receiving additionally a life peerage with the title Baron Millett, of St Marylebone in the City of Westminster.
Millett was well known for his judgment in the House of Lords in the wrongful birth case of McFarlane v Tayside Health Board[14] where a couple were denied recovery of damages for the cost of bringing up an unwanted child, born as a result of a negligently performed vasectomy.
In addition, in a dissenting opinion, he concluded that damages could not be awarded for the pain and distress of pregnancy and delivery but rather that a small sum should be awarded to reflect that the parents had "lost the freedom to limit the size of their family" and thus had been "denied an important aspect of their personal autonomy."