[1] From 1904, Jonynas studied history at the University of Moscow under Matvei Kuzmich Liubavskii, an expert on the Lithuanian Metrica—medieval archives of the Grand Duchy of Lithuania.
Jonynas participated in the Russian Revolution of 1905 and thus had to transfer to the University of Grenoble to study French language and literature.
[2] At the end of World War I, he returned to Lithuania and joined the People's Commissariat of Education of the Lithuanian Soviet Socialist Republic.
[3] After the failure of the Soviet government, he lived in Vilnius, worked as a school principal, and opposed Polish ambitions in the city.
He always critically analyzed primary sources and dismissed secondary sources—thus helping to rid Lithuanian historiography of mistakes, medieval legends and myths, foreign biases and stereotypes.