While still a medical student in the 1880s, Kazys Grinius became a part of a movement for Lithuanian independence from Tsarist Russia. Studying at Moscow University, he was covertly involved in the Lithuanian Student Association, contributed to various publications, and organized demonstrations. He was jailed several times for rioting and anti-Russian activities.

When Lithuania became independent in 1918, Grinius was elected to parliament, serving as Deputy Prime Minister from 1920 to 1922; in 1926 he was elected as President of the Republic.

Grinius' term as president was brief. After only seven months, he was forced out by a military coup, returning to his previous post as medical and sanitary supervisor of Kaunas. During the Nazi occupation he was exiled. After the war, with Lithuania again under Soviet control, he emigrated to America, where he concentrated mainly on writing.

President Grinius died in Chicago in 1950.