Karl Joseph Wirth, known as Joseph Wirth, (6 September 1879 Freiburg im Breisgau – 3 January 1956 Freiburg im Breisgau) was a German politician of the Catholic Centre Party who served as Chancellor of Germany from 1921 to 1922.

The son of a working engineer, he was educated at the University of Freiburg. In 1908 he was appointed to the chair of Economics at the Technical College of Freiburg, and after his election as a municipal councillor in 1911 he devoted himself to financial questions. In 1913 he obtained a seat as a member of the Catholic Centre Party in the diet of Baden, and in 1918 was appointed Minister of Finance. In January 1919 he was elected a member of the Constituent Assembly which sat at Weimar.

In March 1920, when the ministry was reconstructed after the Kapp Putsch, he received the portfolio of finance, which he continued to hold in subsequent ministries. His task was to carry out the system of increased national taxation which his predecessor Matthias Erzberger had induced the Reichstag to adopt. When in May 1921 the Allied ultimatum on reparation was presented to Germany and the sanctions enforced on the Rhine, the Fehrenbach-Simons ministry, which had rejected the London terms, resigned, and Wirth was called upon to form a new cabinet. He succeeded in obtaining the cooperation of a number of able Democrats, Catholics and Socialists, including the prominent industrialist and economist Walther Rathenau as Minister of Reconstructions. Wirth himself retained the portfolio of finance. The new ministry then accepted the Allies' reparation terms — 132 billion marks (£6,600,000,000) payable in yearly instalments of £100,000,000 plus the proceeds of a 25% duty on German exports. By August 31, 1921, Germany had paid the first half-yearly instalment of £50,000,000, and in the following October Rathenau succeeded in concluding a comprehensive agreement with France for paying reparations in kind for the reconstruction of the devastated regions.