Kazys Grinius was born on 17 December 1866 in Selemos Būda village, Sasnava rural district, Marijampolė county.
He went to elementary school in Oškinė (Lymarkai, Marijampolė county), and graduated from Marijampolė Gymnasium. In 1893, he graduated from the Faculty of Medicine at the University of Moscow. During his studies, Kazys Grinius was shortly imprisoned in the Butyrki prison in Moscow for taking part in students' riots (1889).
Still at the University, Kazys Grinius worked as a physician at the anti-cholera station in Minsk in the autumn of 1892.
In 1893, he spent nine months as a ship doctor in the Caspian Sea. In 1894, he began to earn his living as a practicing physician in Marijampolė, in two years moved to Virbalis and later to Naumiestis. From 1898 to 1903 K.Grinius lived in Pilviškiai, then returned to Marijampolė, where again was shortly imprisoned for pro-Lithuanian cultural activity. K. Grinius spent the year 1905 in Vilnius; in 1906 he came back to Marijampolė where he and his wife were imprisoned for two weeks for pro-Lithuanian activity. From 1908 to 1910 he lived in Vilnius. In 1910, Kazys Grinius was again imprisoned in Marijampolė prison for 1.5 months.
From 1914 through to 1919 Kazys Grinius and his family lived in Russia. In 1917 he was elected to the Russian Lithuanian Council in Voronezh. In 1919 he went to Paris, chaired the Repatriation Commission of the Lithuanian delegation; worked for the return of Lithuanians from German captivity, helping around 1,000 of compatriots.
Kazys Grinius returned to Lithuania in 1919. He was a member of the Constituent Seimas, 1st, 2nd and 3rd Seimas; from 19 June 1920 to 2 February 1922, he headed the 6th Cabinet of Ministers. In 1922, Kazys Grinius became director of the Health and Sanitary Division of Kaunas Municipality.
On 7 June 1926, Kazys Grinius was elected President of the Republic of Lithuania and remained in office until the coup d'état on 17 December 1926.
Later he came back to work in Kaunas Municipality.
During the Nazi occupation, Kazys Grinius was exiled to Ažuolų Būda for protesting against the killings of Jews.
In 1944, he fled to the West, arriving to Chicago (USA) in 1947.
Kazys Grinius was one of the leaders of the Peasant Populist Union; an important member of the Varpininkai group (working for the monthly "Varpas" - The Bell); he was among the authors of the program of the Lithuanian Democratic Party (1906).
He edited "Lietuvos ūkininko kalendorius" (Lithuanian Farmer's Calendar), "Ūkininkas" (Farmer), "Varpas", "Sveikata" (Health), "Lietuvos žinios" (Lithuanian News), "Kova su džiova" (Fighting Tuberculosis), "Pieno lašas" (Drop of Milk);
contributed to "Aušrinė" (Morning Star), "Lietuvos ūkininkas" (Lithuanian Farmer), "Vilniaus žinios" (Vilnius News); translated into Lithuanian and published issues No. 1 and 2 of "Lietuvos darbininkas" (Lithuanian Worker).
Kazys Grinius left works on botany, medicine and history, translations of fiction and popular science from Polish and other languages, as well as two volumes of memoirs.
Kazys Grinius died on 4 June 1950 in Chicago.
Algirdas Banevičius. 111 Lietuvos valstybės 1918-1940 politikos veikėjų. 1991
Liudas Truska, Algimantas Lileikis, Gediminas Ilgūnas, Rimgaudas Geleževičius. Lietuvos prezidentai. Vilnius 1995