Beginning in 1997, Kościński was a director of Bank Zachodni WBK SA. He previously work for several Polish Banks, and has also held positions in the international finance sector in London, United Kingdom. From November 2015 to November 2019, he was Undersecretary of State at the Ministry of Development, the Ministry of Entrepreneurship and Technology and the Ministry of Finance, consequetively. He has also been the representative of the Prime Minister at the Polish regulatory authority for the finance sector.[4]