João Tamagnini de Sousa Barbosa (December 30, 1883 – December 15, 1948), commonly known by João Tamagnini Barbosa (), or Tamagnini Barbosa, was a Portuguese military officer and politician of the Portuguese First Republic (1910–1926). He served as Minister of Interior, Colonies and Finances during the period known as "New Republic", after the coup d'état of the National Republican Party ("Sidonist Party") and the semi-dictatorial government of President/Prime Minister Sidónio Pais, followed by a brief participation in the provisional government of João do Canto e Castro after the assassination of Sidónio Pais.