During the inter-war period, he was Minister of Transport during the Second MacDonald ministry, then after losing his parliamentary seat in the 1931 general election, he became Leader of the London County Council in the 1930s.

After returning to the Commons, he was defeated by Clement Attlee in the 1935 Labour Party leadership election but later served as Home Secretary in the wartime coalition.

Attlee, Morrison, Ernest Bevin, Stafford Cripps, and initially Hugh Dalton formed the "Big Five" who dominated those governments.

His early politics were radical, and he briefly flirted with the Social Democratic Federation over the Independent Labour Party (ILP).

Both he and his supporter Hugh Dalton put some of the blame on the Masonic New Welcome Lodge, who, they claimed, backed the third-place leadership candidate Arthur Greenwood and then switched their votes to Attlee.

[12] In 1940, Morrison was appointed the first Minister of Supply by Winston Churchill, but shortly afterwards succeeded John Anderson as Home Secretary.

The arrival of black American troops caused concern in the government, leading Morrison, the Home Secretary, to comment "I am fully conscious that a difficult social problem might be created if there were a substantial number of sex relations between white women and coloured troops and the procreation of half-caste children."

[17] Following the end of the war, Morrison was instrumental in drafting the Labour Party's 1945 manifesto Let us Face the Future.

[18][19] Labour won a massive and unexpected victory, and Morrison was appointed Leader of the House of Commons, having switched his own seat to Lewisham East.

As Lord President he chaired the committee on the Socialization of Industries, and followed the model that was already in place of setting up public corporations, such as the BBC in broadcasting (1927).

[20][21] In July 1946, Morrison, together with US ambassador Henry F. Grady proposed "The Morrison-Grady Plan", intended to resolve the Palestine conflict, calling for federalisation under overall British trusteeship.

[22] His tenure there was cut short by Labour's defeat in the 1951 general election, and he was appointed a Member of the Order of the Companions of Honour in November that year.

[23] Morrison lacked a deep concern for foreign affairs, but he was an enthusiastic leader of a major domestic project, the Festival of Britain.

The Labour government was losing support, and the implicit goal of the festival was to give the people a feeling of successful recovery from the war's devastation, as well as promoting British science, technology, industrial design, architecture and the arts.

[3] During 1961–65, Morrison was Director of the FCI News Agency,[28] an organisation reporting on events behind the Iron Curtain and run by exiles from Marxist regimes such as the journalist Josef Josten.

While working in a market garden in Letchworth during World War One, Morrison met his first wife, Margaret Kent (1896–1953), a secretary and daughter of a railway clerk.

His total involvement in politics, however, meant that theirs was not a happy marriage; his later autobiography made no mention of Kent or their daughter, Mary.

[3] Morrison had a protracted affair with Labour MP and Minister Ellen Wilkinson, who died in 1947, although views differ as to whether this was a platonic or sexual relationship.

[3] Morrison's grandson Peter Mandelson was a cabinet minister in the Labour governments of Tony Blair and Gordon Brown.

In the 1977 Granada TV play Philby, Burgess and Maclean by Iain Curteis, Arthur Lowe appeared as Morrison – glowering to the camera in his final shot to show the opaque right lens of his spectacles.