Jonas Vileišis pronunciation (January 3, 1872 – June 1, 1942) was a Lithuanian lawyer, politician, and diplomat.
Vileišis was born in Mediniai, near Pasvalys. In 1892 he graduated from the Šiauliai gymnasium. During 1892-1894, he studied physics and mathematics at Saint Petersburg University. Later he transferred to the study of law, graduating in 1898. As a student he began contributing to the newspapers Varpas (The Bell) and Ūkininkas (The Farmer). From 1896 to 1898 he was a member of the Social Democratic Party of Lithuania. After returning to Lithuania, he began practicing law and joined the 12 Apostles organization, dedicated to defending the right to use the Lithuanian language in print, which was banned at the time. In 1902 he participated in the creation of the Lithuanian Democratic Party.
After the ban on Lithuanian language was lifted in 1904, Vileišis obtained permission to publish the newspaper Lietuvos Ūkininkas and was its editor-in-chief from 1905 to 1906. From 1907 to 1909, he served as the publisher of Vilniaus žinios (Vilnius News) and, after it was banned, published and edited Lietuvos Žinios (Lithuanian News). He was one of the organizers of the Great Seimas of Vilnius in 1905, and an organizer of the Lithuanian Science Society in 1907.