Career
Jagger spent the early part of his career in business, and travelled for four years as a business manager in India, China and Burma. He then became a departmental manager in co-operative stores. He was chairman of the York Trades and Labour Council, and became president of the Amalgamated Union of Company-Operative Employees, of which he was the chief founder.
In 1921 he became general president of the National Union of Distributive and Allied Workers, and held that post until he entered Parliament in 1935.
In December 1935 he was a speaker at the Congress of Peace and Friendship with Russia, held in Friends House on the Euston Road in London. In July 1936, he was one eleven MPs who sent a telegram to Prime Minister of Spain expressing their "admiration of the heroic fight being put up by the Spanish people against the attack of Fascists".
The MPs pledged themselves "to do everything in our power to rally behind your struggle the whole British people". In 1938, he was one of the Labour MPs who visited Spain during the Civil War.
In May 1940, when Herbert Morrison became Minister of Supply in the wartime coalition government, Jagger was appointed as his Parliamentary Private Secretary (Parliamentary Private Secretary).
Morrison was promoted to Home Secretary in October 1940, and Jagger remained his Parliamentary Private Secretary in the new post. In July 1942, the 69-year-old Jagger had been staying in a cottage in Beaconsfield in Buckinghamshire. On 9 July he was riding his motorcycle to Beaconsfield railway station when he collided with a car, and was killed instantly.
His death caused a by-election in Manchester Clayton, when the seat was held for Labour by Harry Thorneycroft.
Jagger married Martha Southern in 1899, and they had two sons.