On 30 March 2017, Dr Janusz Fiszer was appointed to the Supervisory Board of mBank S.A. as an independent member. mBank S.A. is the fourth-largest bank in Poland and is listed on the Warsaw Stock Exchange; its corporate parent, Commerzbank A.G., is the second largest bank in Germany.

Dr Janusz Fiszer, partner, attorney and certified tax advisor, heads GESSEL's tax law practice. He specializes in international tax law and in tax aspects of M&A transactions.

A graduate of the University of Warsaw Law School, holds a doctorate in law. Since 1980, lecturer at the University of Warsaw’s Faculty of Management, currently an associate professor. Dr Fiszer is also a lecturer in international tax law in the postgraduate program on international tax strategies at the Main Economic University (SGH) in Warsaw.

Dr Fiszer is consistently listed in international and Polish directories of law firms and lawyers – "Chambers Global", "Chambers Europe", "PLC Which Lawyer?", "World Tax – Ranking of Tax Advisory Firms and Tax Advisors", " Who’s Who Legal – The International Who’s Who of Business Lawyers", "Rzeczpospolita", "Dziennik Gazeta Prawna" and "Forbes".

In 2016, in the 10th edition of the Tax Advisory Firms Ranking of the Rzeczpospolita daily which ranks the leading Polish tax experts and largest tax advisory operations, Dr Janusz Fiszer was named as “Tax Advisor of the Decade in the International Tax Law”.