Lennox-Boyd was educated at Sherborne School, Dorset and graduated from Christ Church, Oxford, with a Master of Arts and gained the rank of Lieutenant in 1940 in the service of the Royal Naval Volunteer Reserve.

He was elected as Member of Parliament (MP) for Mid Bedfordshire in 1931 (at the age of 26), and was admitted to Inner Temple, as a barrister in 1941.

He was a member of Winston Churchill's government as Minister for Transport and Civil Aviation from 1952 to 1954, when he became Secretary of State for the Colonies, where he saw in the first stages of decolonisation in Africa, with the granting of independence to Cyprus, Ghana, Iraq, Malaya, Sudan. He also oversaw the period of the Mau Mau Rebellion in Kenya, and was persuaded to stay in office by Harold Macmillan after being censured for the Hola disaster. However, after the 1959 general election he was replaced as Colonial Secretary with Iain Macleod. Lennox-Boyd also made up himself as the first Secretary of the States for the Colonies that talk openly towards independent for the Federation of Malaya, he invited the then Chief Minister of Malaya, Tunku Sir Abdul Rahman Al-Haj and his fellows to Lancester House to make up the possibility for Malaya to achieve as a sovereign nation.

As secretary of state for transport, he once memorably opined that road accidents were the result not of the taking of large risks, but of the taking of small risks very large numbers of times - a pertinent observation which is still valid today.

Soon after his replacement he was created the first Viscount Boyd of Merton of Merton-in-Penninghame, co. Wigtown, on 8 September 1960, thereby causing a by-election for his Mid Bedfordshire constituency which was won by Stephen Hastings. Being opposed to the line taken in Harold Macmillan's Wind of Change speech, he subsequently became an early Patron of the Conservative Monday Club.

He held the office of Deputy Lieutenant of Bedfordshire between 1954 and 1960 and Deputy Lieutenant of Cornwall in 1965. He was managing director of Arthur Guinness & Sons between 1959 and 1967.

He married Lady Patricia Guinness, daughter of Rupert Guinness, 2nd Earl of Iveagh, on 29 December 1938. They had three children:

• Simon Lennox-Boyd, 2nd Viscount Boyd of Merton (b. 7 December 1939)
• Christopher Lennox-Boyd (b. 22 July 1941)
• Mark Lennox-Boyd (b. 4 May 1943)