When Poland regained independence in November 1918, Jędrzejewicz began work at the Polish Army's Section II (Oddział II, or Intelligence).
On 24 April 1920, Jędrzejewicz, now a captain, signed a military convention with Ukraine's AtamanSemen Petlura which paved the way for the Polish Army's 1920 Kiev Expedition. Next he served as Section II chief successively to Generals Kazimierz Sosnkowski and Gustaw Zygadłowicz. In September–November 1920, as a major, he was the Polish Army's liaison officer to allied Belarusian forces.
Returning to Poland, he served as director of the Foreign Ministry's Consular Department (1928-1933) and as Treasury Vice Minister (1933-1934). On 22 January 1934, he was appointed Minister of Religious Denominations and Public Education in the government of his brother, PremierJanusz Jędrzejewicz (1885-1951), serving on as well in the premierships of Leon Kozłowski and Walery Sławek. He introduced educational reforms that sparked controversy in Poland but won international approval and emulation.
After Marshal Józef Piłsudski died (1935), Jędrzejewicz held no more ministerial offices.
When World War II broke out in September 1939, Jędrzejewicz helped evacuate the treasury of the Fund for National Defense, which in February 1940 was delivered to General Władysław Sikorski's Polish government-in-exile in Paris. Due to the anti-Piłsudskiite policies of General Sikorski (whose prewar career had been derailed by differences with Piłsudski), Jędrzejewicz was prevented from serving now with the Polish Armed Forces in exile. Consequently, in March 1941 he emigrated to New York City.
On 4 July 1943, Jędrzejewicz co-founded the Józef Piłsudski Institute of America, dedicated to studying recent Polish history, and was its first director (5 July 1943 — 28 September 1948).
Jędrzejewicz published some 300 scholarly papers in history and several major books, including Poland in the British Parliament, 1939-45 and a two-volume Kronika życia Józefa Piłsudskiego (Chronicle of the Life of Józef Piłsudski). His English-language publications also included Piłsudski: a Life for Poland, New York, Hippocrene Books, 1982.
"Jędrzejewicz, Wacław," Who's Who in Polish America, 1st ed., 1996–1997, New York, Bicentennial Publishing Corp., distributed in the book trade by Hippocrene Books, 1996, pp. 173–74.