An Independent Labour Party (ILP) member, he was elected as Member of Parliament (MP) for Linlithgowshire at the 1922 general election.

In 1924 he was Secretary for Mines (not a Cabinet-level post) in the First Labour Government.
He lost his seat in 1924, but was re-elected for Linlithgowshire at a by-election in 1928.

In the second Labour Government of 1929–31 Ramsay MacDonald appointed him Financial Secretary to the War Office (1929–30); Cowling says that MacDonald believed he had rescued Shinwell's ministerial career when no minister would take him.
He then served again as Secretary for Mines from 1930–1.
At the time Shinwell was an admirer of MacDonald and tried to dissuade him from forming a National Government in 1931.
He again lost his seat at the general election that year.

He returned to the Commons in 1935 after defeating MacDonald for Seaham Harbour, County Durham (later renamed Easington after boundary changes in the late 1940s).

He campaigned vigorously, along with left-wingers such as Aneurin Bevan, for Britain to support the Popular Front government in Spain against Franco in the Spanish Civil War.
On 4 April 1938, during a heated House of Commons debate in which he had been criticising the government's foreign policy, he struck Conservative MP Commander Robert Tatton Bower in the face- causing internal bleeding and a burst eardrum- after Bower told him to "go back to Poland!".
Shinwell said he had taken this to be an anti-semitic remark.

In May 1940 he refused a position in Winston Churchill's Coalition Government in the Ministry of Food.
He became chairman of the Labour Party in 1942.
During the Second World War he was a vigorous but patriotic backbench critic of Churchill.
He and Earl Winterton, another serial critic of the government, were known as "Arsenic and Old Lace".
An Independent Labour Party (ILP) member, he was elected as Member of Parliament (MP) for Linlithgowshire at the 1922 general election.
In 1924 he was Secretary for Mines (not a Cabinet-level post) in the First Labour Government. He lost his seat in 1924, but was re-elected for Linlithgowshire at a by-election in 1928.
In the second Labour Government of 1929–31 Ramsay MacDonald appointed him Financial Secretary to the War Office (1929–30); Cowling says that MacDonald believed he had rescued Shinwell's ministerial career when no minister would take him. He then served again as Secretary for Mines from 1930–1. At the time Shinwell was an admirer of MacDonald and tried to dissuade him from forming a National Government in 1931. He again lost his seat at the general election that year.
He returned to the Commons in 1935 after defeating MacDonald for Seaham Harbour, County Durham (later renamed Easington after boundary changes in the late 1940s).
He campaigned vigorously, along with left-wingers such as Aneurin Bevan, for Britain to support the Popular Front government in Spain against Franco in the Spanish Civil War. On 4 April 1938, during a heated House of Commons debate in which he had been criticising the government's foreign policy, he struck Conservative MP Commander Robert Tatton Bower in the face- causing internal bleeding and a burst eardrum- after Bower told him to "go back to Poland!". Shinwell said he had taken this to be an anti-semitic remark.
In May 1940 he refused a position in Winston Churchill's Coalition Government in the Ministry of Food. He became chairman of the Labour Party in 1942. During the Second World War he was a vigorous but patriotic backbench critic of Churchill. He and Earl Winterton, another serial critic of the government, were known as "Arsenic and Old Lace".
Manny Shinwell