In 1894 he graduated from the Second High School in Vilna and began studying mathematics and physics at Imperial Moscow University.

Between November 1903 and September 1904, Prystor served in the 16th Sapper Battalion of the Imperial Russian Army.

Sometime in the early 20th century, Prystor joined Polish Socialist Party, and became a close associate of Józef Piłsudski.

In 1904 Prystor, together with Jozef Kwiatek, Walery Sławek and Boleslaw Jedrzejowski, organized public protests against the forcible draft of ethnic Poles into the Russian Army to fight in the Russo-Japanese War.

Using the pseudonym Katajama, he organized groups of activists in Warsaw, and in March of that year, he carried out the assassination of Russian Police Officer Karl Nolken.

Later on, he participated in a number of raids of the Combat Organization, including bank robberies, terrorist attacks on soldiers and police officers and acts of sabotage.

Released after the February Revolution (March 17, 1917), he continued working for the Polish Socialist Party.

After the capture of Minsk by the Imperial German Army (May 1918), Prystor came to Warsaw, to join Polish Military Organisation.

Together with other activists, he prepared the assassination of General Hans Hartwig von Beseler, but the attack was cancelled.

On November 10, 1918, Prystor was among the officials who welcomed Józef Piłsudski at Warszawa Główna railway station.

Before the Battle of Warsaw (1920), he was recalled from the frontline by Józef Piłsudski and became the personal assistant of the Polish Marshal.

Furthermore, he dissolved the structures of the government health insurance program, which were in the hands of oppositional Polish Socialist Party.

In 1931, he was elected to the Sejm, as a member of the pro-government Nonpartisan Bloc for Cooperation with the Government (BBWR), remaining in the Polish Parliament until 1935.

In 1934, Prystor went on a private trip to Lithuania, during which he talked with main Lithuanian politicians, including President Antanas Smetona.

On March 9, 1939, he gave a speech, harshly criticizing the policies of the government and the Camp of National Unity.