Born to a family of affluent farmers in Suvalkija, Prapuolenis was an active member of the Ateitininkai Catholic youth movement and a vocal opponent of the authoritarian regime of President Antanas Smetona.

For organizing a student strike to demand democracy, he was expelled from the Klaipėda Commerce Institute and given a four-year prison sentence in December 1938.

However, he was allowed to resume his studies due to the changing political situation in the aftermath of the German ultimatum to Lithuania of March 1939.

When Germany invaded the Soviet Union and LAF members started the uprising, Prapuolenis read the independence proclamation at 10:35 a.m. on 23 June 1941 at the Kaunas radio station.

But when Prapuolenis protested the German decision to disband the Provisional Government, he was arrested by the Gestapo and sent to the Dachau concentration camp.

[3] He applied to study at the War School of Kaunas instead, but his request was rejected due to his political activity and opposition to the regime of President Antanas Smetona.

When the new coalition government led by Jonas Černius, which included members of the Lithuanian Christian Democratic Party and Lithuanian Popular Peasants' Union, was formed in March 1939, Prapuolenis returned to his studies at the institute which was relocated to Šiauliai as Lithuania lost Klaipėda to Nazi Germany.

[5] Together with Adolfas Damušis, brigade general Motiejus Pečiulionis, and others, Prapuolenis established resistance groups (a network of fives) of the Lithuanian Activist Front (LAF) in Kaunas.

[5] Despite the German prohibitions, he participated in developing strategy of the Lithuanian Front (LF), an anti-Nazi and anti-Soviet resistance group that replaced LAF.

Between 15 September and 8 October 1944, Prapuolenis together with Zenonas Ivinskis and Pranas Padalskis secretly visited German-occupied Lithuania and met anti-Soviet resistance members of LF and the Lithuanian Liberty Army in Telšiai, Rietavas, and Kretinga.

[3] Prapuolenis published articles in various Lithuanian periodicals, including XX amžius (20th century), Studentų dienos (The Days of Students), Į laisvę (Towards Freedom), Tėvynės sargas (Guardian of the Fatherland).