The Piłsudski Institute of America, a research organization and archive, came into being during the General Assembly of the National Committee of Americans of Polish Extraction (KNAPP), held at the Washington Hotel in New York City on July 3–4, 1943.

Jędrzejewicz commented on that event in one of his press releases: "Taking advantage of the presence of several prominent Polish émigré activists, we decided to bring to fruition a plan that had been in the works for a long time, namely, to call into existence on July 4 the Józef Piłsudski Institute, dedicated to the research of the most recent history of Poland."

The organizers of the New York research center were keenly aware of the importance of collecting documents related to such a crucial period in Polish history as World War II.

After displacing the Red Army from the eastern regions of Poland, the Nazis occupied the entire country; their aim was the destruction of Polish scholarship and cultural heritage.

At the organizational meeting of the institute, the following decisions were taken: Franciszek Januszewski was named head of the Organization Committee, Ignacy Matuszewski his deputy, Marta Kozłowska from New Jersey secretary and Józef Piech treasurer.

At the second meeting of the Committee on September 16 of that year, Januszewski resigned as president and was replaced on an interim basis by Ignacy Matuszewski until the General Assembly of all members and the election of a new board.

During the summer Jędrzejewicz toured areas with large Polish populations (including Detroit, Chicago, and Philadelphia), giving presentations, explaining the goals and the reasons behind the institute, and recruiting new members.

As a result, the institute received a valuable collection of books and documents related to World War II and the activities of Polish groups in France, Great Britain, and the Near East.

The original intent of reconstructing the institute which had existed before the war in Warsaw was not feasible because of the Yalta Agreement, which left the Polish nation for the next half-century within the Soviet sphere of influence.

From the end of the 1940s, when the National Committee of Polish-Americans ceased to exist, the activities and statements by leaders of the institute were perceived as sui generis instructions for the independence circles.

These people formed a highly cohesive group, which (faithful to Marshal Piłsudski's ideals) refused to accept any compromise concerning Poland's independence and the integrity of her borders.

They rejected the position espoused by then-Prime Minister Stanisław Mikołajczyk which promoted accepting the Treaty of Yalta and the Provisional Government of National Unity (TRJN) and later took a firmly anti-communist stand, refusing all contacts with organizations in the Polish People's Republic (PRL).

Due to their efforts, financial support, and fundraising initiatives, the institute survived and eventually flourished, developing its activities in publishing and cataloging its extensive collection.

Efforts were made to single out independent scholars and researchers who, after their return to Poland, would present an unbiased picture of World War II without the communist ideological influence.

Inspiring a truly independent thought process in Poland only became possible in the 1970s and '80s, however, when the institute developed its own scholarship program supporting young scholars belonging to non-communist political groups.

With the assistance of Jan Malicki (editor of the magazine Przegląd Wschodni), some books found their way to libraries and schools in the former Polish eastern regions of present-day Ukraine and Belarus.

Other English-language publications of scholars connected with the institute are those of Marian K. Dziewanowski, Janusz K. Zawodny, Stanisław Blejwas, Piotr Wandycz, Anna Cięciała and Tytus Komarnicki.

The research materials assembled at the institute have been used in exhibitions, films, and publications including Bitter Glory by Richard M. Watt; The Heart of Europe: A Short History of Poland by Norman Davies; The Exile Mission: The Polish Political Diaspora and Polish Americans 1939–1956 by Anna Jaroszyńska-Kirchman; the US Holocaust Memorial Museum's internet exhibit Fight and Rescue; and the film The World was Ours: The Jewish Legacy of Vilna, directed by Mia Van Doren.

They illustrate the activities of American Polonia and include materials and documents offered by prominent statesmen, politicians, and military personalities such as historian Władysław Pobóg-Malinowski (who died in France but left his archive in New York).

It includes works by noted Polish painters Jan Matejko, Juliusz Kossak, Józef Brandt, Wojciech Gerson, Leon Wyczółkowski, Aleksander Gierymski, Julian Fałat, Jacek Malczewski and Stanisław Wyspiański.