Stauning was trained as a cigar sorter and soon became involved with trade union activity. From 1896 to 1908 he was leader of the Cigar Sorters' Union, in 1898-1904 also editor of the magazine Samarbejdet (Co-operation) of the Federation of Trade Unions, and elected Member of Parliament (Folketinget) in 1906.
In 1910 he was elected chairman of the Social Democratic Party, a position he retained for almost thirty years, until 1939. After participating as minister of the coalition cabinet serving 1913-1920, he returned to government as prime minister in 1924 - for a minority cabinet which would survive until 1926. His cabinet was considered ground breaking not only as it was the first purely Social Democratic cabinet, but also because a woman, Nina Bang, was appointed Minister of Education, which attracted some international attention.
From 1929 he led the successful coalition cabinet with the Social Liberal Det Radikale Venstre party that would steer Denmark out of the Great Depression, shaping a major political compromise that greatly improved the Danish economy, and also transformed the Social Democratic Party from a class party to a popular party.
Under Stauning's leadership Denmark, like the other Scandinavian countries, developed a social welfare state. It's often proposed that the longlived coalition cabinet, and its successful policies, actively averted the Communist and Fascist movements that were sweeping much of Europe from developing a strong following in Denmark.
Stauning's second cabinet lasted until Operation Weserübung, the Nazi occupation of Denmark commenced April 9, 1940, when the cabinet was widened to include all political parties. Contrary to most other governments of the Nazi-invaded countries, king Christian X of Denmark and his government ordered the defence forces to give up resistance, and chose to remain in their country also under the occupation, which is believed to have contributed to the Nazi years being more lenient in Denmark than in other countries under Hitler's control.
Thorvald Stauning died two years later deeply depressed about the future of Social Democracy in a Nazi-dominated Europe.
Like many other workers' leaders of his generation, as for instance Hjalmar Branting in Sweden, Stauning was a charismatic leader who was widely respected in his country playing an immensely important role in integrating Danish society after the social changes following the Industrial Revolution and common suffrage. There are many reasons to consider him the greatest figure in 20th century Danish politics.