Janusz Krupski was born in 1951 in Lublin. As a student, he joined the ant-communist opposition movement at the Catholic University of Lublin, where in 1973, as president of the Historians' Circle, he opposed the transformation of the Association of Polish Students into the Socialist Union of Polish Students.
In June 1976, he handed over an open letter to the participants of the European Youth and Students' Assembly in Warsaw, concerning incidents of human rights violations in communist Poland. Thanks to his cooperation with Piotr Jegliński, he discovered a way of transferring information about opposition activities in the Polish People's Republic to the West. He was a co-founder of the NOWA Independent Publishing House, the first underground publishing house in the 1970s.
In the autumn of 1977, he began publishing the "Spotkania" magazine - one of the most important independent publications. It was on the pages of this magazine that texts by priests Franciszek Blachnicki and Józef Tischner, as well as Władysław Bartoszewski and Stefan Kisielewski appeared. The magazine was also reprinted in France, where Piotr Jegliński founded the Editions Spotkania publishing house. The community of "Spotkania", both in Poland and abroad, published many important books on Polish history.
After the "Solidarity" movement was legalized, Janusz Krupski became the coordinator of the Historical Section at the Inter-Enterprise Founding Committee in Gdańsk. The result of his documentation work was the book "Grudzień 1970" [December 1970] , published by Editions Spotkania in Paris (1987).
He was in hiding during Martial Law. Arrested in the autumn of 1982, he was interned in Lublin. At that time, he rejected the Security Services proposal to issue the "Spotkania" magazine officially. A few weeks after his release from internment, he was abducted by the Security Services, taken to the Kampinos Forest and doused with a caustic substance, as a result of which he suffered severe burns.
In free Poland, he was an expert in the parliamentary commission investigating the effects of Martial Law and in the Committee on Constitutional Responsibility. He also continued publishing activities. In 2000 he was appointed Deputy President of the Institute of National Remembrance. In 2006, he assumed the position of the head of the Office for Veterans and Victims of Oppression.
He died in the crash near Smolensk on 10 April 2010, on his way to the celebration of the 70th anniversary of the Katyn Massacre. He was posthumously awarded the Grand Cross of the Order of Polonia Restituta.