Born on 1 June 1960 in Chrośnica. Szczepański graduated from the Poznań University of Economics with a degree in organisation and management. His career as a public servant started at the local government level when he was elected to the Leszno City Council in the 1994 elections, where he served as the Deputy Chairman of the Council and the Head of the Audit Committee until 1998.

In 1996 he was elected Member of the Polish Parliament, and continued to serve throughout the 1997–2001 term of office. In October 2001, he was appointed Deputy Head of the Housing and Urban Development Authority. In 2004–2005, he worked as Undersecretary of State at the Ministry of Infrastructure.

He was re-elected to the Polish Parliament in the 2005 election, and won election again in the snap election of 2007. From 2012 to 2021, he was an advisor to the management board of Poczta Polska SA. In 2014, he was elected a councillor of the Greater Poland Voivodeship Assembly. After another local election, he served as chairman of the Greater Poland Voivodeship Assembly in 2018–2019.

In 2019 he was elected to the Polish Sejm, representing the Democratic Left Alliance (SLD), and throughout his term of office, he served as chairman of the Parliamentary Committee on Administration and Internal Affairs. In 2023, he was re-elected from the Kalisz-Leszczyna electoral district.

He is a deputy chairman of the Greater Poland branch of the New Left party and a member of the party's national board.