Justice Janusz Niemcewicz was born on 28 July 1949 in Siemianowice Šl±skie. Graduated from the Faculty of Law and Administration of the Silesian University in Katowice in 1971. From 1971 to 1973 completed a court training and worked as an associate judge in the District Court in Katowice from 1973 to 1974. Between 1974 and 1978 completed the bar training. Attorney at law from 1978 to 1995. Member of the General Council of the Bar from 1995 to 1997. Between December 1997 and January 2001 Undersecretary of State in the Ministry of Justice.
From 1993 to 1997 Deputy to the Sejm of the Republic of Poland where he served on the Rules and Deputies' Affairs Committee, Justice and Human Rights Committee and the Special Committee on Codification of Penal Law, and on the Constitutional Accountability Committee.
Actively involed in drafting of bills improving and adjusting the existing legislation to the requirements of the 1997 Constitution (in particular a bill on the system of common courts, the Penal Code and the Commercial Companies Code).
Janusz Niemcewicz was a Justice of the Constitutional Tribunal from 2001 to 2010 and Vice-President of the Constitutional Tribunal from 2008 to 2010.