The Weimar Coalition (German: Weimarer Koalition) is the name given to the centre-left to center-right coalition of the Social Democratic Party of Germany (SPD), the social liberal German Democratic Party (DDP) and the Christian democratic Centre Party, who together had a large majority of the delegates to the Constituent Assembly that met at Weimar in 1919, and were the principal groups that designed the constitution of Germany's Weimar Republic. These three parties were seen as the most committed to Germany's new democratic system, and together governed Germany until the elections of 1920, when the first elections under the new constitution were held, and both the SPD and especially the DDP lost a considerable share of their votes. Although the Coalition was revived in the ministry of Joseph Wirth from 1921 to 1922, the pro-democratic elements never truly had a majority in the Reichstag from this point on, and the situation gradually grew worse for them with the continued weakening of the DDP. This meant that any pro-republican group that hoped to attain a majority would need to form a "Grand Coalition" with the conservative liberal German People's Party (DVP).
Nevertheless, the coalition remained at least theoretically important as the parties most supportive of republican government in Germany, and continued to act in coalition in the government of Prussia and other states until as late as 1932. In the second round of voting in the 1925 presidential election, the Weimar Coalition parties all supported the candidacy of the Centrist former chancellor Wilhelm Marx, who was narrowly defeated by Field Marshal Paul von Hindenburg, supported by a center-right coalition of the DVP, the German National People's Party, and the Bavarian People's Party.
After World War II the reconstituted SPD and the de facto successors of the Centre Party (Christian Democratic Union and Christian Social Union) and the DDP (Free Democratic Party) formed the main political basis of the democratic Bundestag of West Germany.
The elections of 6 June 1920 resulted in severe decline in the Coalition's parliamentary strength, despite hopes that the dramatic failure of the right-wing Kapp Putsch would lessen the political reorientation of the Reichstag parties. The SPD received 21.7% of the vote, a significant drop from the 37.9% it had in January 1919. The DDP suffered the greatest loss, dropping from 18.5% to 8.4%. The Centre Party received 13.6% of the vote, only a slight decline from the 15.1% it had previously held.