He graduated from the Faculty of Law and Administration at the Jagiellonian University (1979). In 1980 Marian Banaś completed postgraduate studies in religion, he also studied philosophy at the Pontifical Academy of Theology. He completed court application in 1996 finalized with judge exam and the Supreme Audit Office (NIK) application. He also completed postgraduate studies in Internal Audit (2009-2010).
Mr. Banaś was one of the founders and activists (from 1976 to 1980) of Action for the Independence and the Institute of Katyń. From 1981 to 1983 Marian Banaś was serving a prison sentence for activities in the "Solidarity". In 1990, he was awarded the Knight's Cross of the Order of Polonia Restituta by the Polish government in exile, and in 2011 the Officer's Cross of the Polish Order of Polonia Restituta by the Polish President. He was also awarded the Medal "Firm in the Word". In 2015 President of Poland Andrzej Duda awarded him the Cross of Freedom and Solidarity.
Marian Banaś advised the Minister of the Interior during the government of Jan Olszewski. In the years 1992-2015 he worked in the Supreme Audit Office occupying various positions (including the chief specialist and legal counsel). From November 21, 2005 to January 2, 2008 he held the function of Undersecretary of State in the Ministry of Finance and since November 28th, 2005 he was also the Chief of the Customs Service.
He practices sports and is a fond karate coach.