UEFA were investigating his presence at an event organised in Katowice on Monday, saying they "abhor the values that are promoted by the group", but kept him on as the referee after an apology and clarification from an anti-discrimination body NEVERAGAIN.
Marcinak, who refereed the World Cup final in December between Argentina and France and is seen as one of Europe's top referees, took part in an event called Everest, which was organised by Slawomir Mentzen, known for creating a beer named 'White IPA Matters' in 2021, which mocked the Black Lives Matter movement.
He is also the leader of the Confederation Party in Poland, who are publically right-wing and nationalist with the political slogan upon launch of: “We stand against Jews, gays, abortion, taxation and the European Union”.
Marcinak said in a statement that was sent to UEFA: "Upon reflection and further investigation, it has become evident that I was gravely misled and completely unaware of the true nature and affiliations of the event in question.
"I had no knowledge that it was associated a Polish extreme-right movement. Had I been aware of this fact, I would have categorically declined the invitation.
"It is important to understand that the values promoted by this movement are entirely contrary to my personal beliefs and the principles I strive to uphold in my life. I am deeply remorseful for any perception that my participation may have contradicted them..."
He added: "Moving forward, I pledge to be more vigilant in scrutinising the events and organisations with which I associate myself. I am committed to learning from this experience and ensuring that such lapses in judgment do not occur in the future."
During their investigation, UEFA said they had reached out to 'NEVERAGAIN', an NGO affiliated with the FARE network, which counters discrimination in European football.
"(They) raised the initial concerns about Mr Marciniak's involvement in the event," UEFA said.
"They requested that Mr Marciniak remain in his role as the referee for the upcoming UEFA Champions League final, firmly asserting that removing him would undermine the promotion of anti-discrimination."