Tomasz Greniuch (1982^[1]-) is a Polish historian, formerly employed by the Institute of National Remembrance. In his youth he was associated with far-right groups which caused a media controversy in 2021.

Greniuch is among the great-grandsons of Józef Piłsudski.^[2] He graduated in history from the University of Opole and received his doctorate from the Catholic University of Lublin on the cursed soldiers who fought under the command of Henryk Flame.^[3] An active cadre of National Radical Camp (ONR) — a fascist anti-semitic ultranationalist organization — and spokesperson of its Opole circle, Greniuch commemorated anti-Jewish pogroms, greeted others with the Nazi salute, and raised^{[clarification needed]} White supremacist slogans.^[3][4][5] On an occasion when he was investigated by the local police and threatened with expulsion by the university, he defended the Nazi salute, claiming that it was a pan-nationalist greeting with its origins among the Romans and he cannot be blamed for its usurpation by Hitler.^[3]

In 2018, Greniuch joined the Institute of National Remembrance (IPN) as a historian.^[2][6] In an interview in 2019, Greniuch maintained subscribing to ONR's views but lamented having to temper his behaviour in light of professional commitments.^[5]

On 9 February 2021, the incumbent Law and Justice Party government appointed Greniuch as the acting head of the Wroclaw branch of the IPN.^[7] The decision spurred controversy and drew sharp criticism from the political opposition, historians, journalists, survivors of the Holocaust, and Israel.^[7] In response, Greniuch tendered an apology for his "youthful bravado" and cited a list of relatives who fell victim to the Nazis;^[2] though the IPN initially upheld his appointment, highlighting his apology and freedom of speech, a fortnight later, they accepted his resignation and dismissed him for corroding public trust in the institution.^[3][7][8]