Noel-Baker was born to a Canadian-born Quaker father, Joeseph Allen Baker, who moved to England to set up a manufacturing business and himself served on the London City Council and in the House of Commons. Initially educated in the US at the Quaker-associated Haverford College, he attended King's College, Cambridge from 1910 to 1912, where as well as being an excellent student he became president of the debating society and the Cambridge University Athletic Club. He was selected and ran for Great Britain at the Stockholm Olympic Games, and was team manager as well as a competitor for the British track team for the 1920 and 1924 Olympics. In 1920 at Antwerp he won a silver medal in the 1500 metres. The exploits of the British team at the 1924 Games were later made famous in the 1982 film Chariots of Fire, though Noel-Baker's part in such was not portrayed in that film.
During the First World War, Noel-Baker organised and commanded several Ambulance Units, for which he received military medals from France and Italy as well as his own country.
After the war, Noel-Baker was heavily involved in the formation of the League of Nations, serving as assistant to Lord [[Robert Cecil]], then assistant to Sir Eric Drummond, the league's first secretary-general.
His political career with the British Labour Party began with an unsuccessful tilt at a House of Commons seat in 1924. He was elected as the member for Coventry in 1929, which he held to 1931. From 1936 to 1950 he served as the member for Derby, and from 1950 to 1970 as the member of Derby South. As well as a parliamentary secretary role during World War II under Winston Churchill, he served in a succession of junior ministries in the Atlee Labor Government. He was also prominent in the organizational wing of the party, serving as party chairman in 1946.
In the mid-1940's, Noel-Baker served on the British delegation to what became the United Nations, helping to draft its charter and other rules for operation as a British delegate.
Noel-Baker also spent time as an academic early in his career, as a professor of international law at the University of London from 1924 to 1929 and as a lecturer at Yale University in 1933-34.
Noel-Baker married Irene Noel, a field hospital nurse, in 1915, adopting the hyphenated name in 1943. Their only son, Francis Noel-Baker, also became a parliamentarian and served together with his father in the Commons.