In 1989, he ran unsuccessfully for the Senate as a representative of Skierniewice Province. In subsequent elections (1991), Miller was a leader on the election list of the Social Democracy of the Polish Republic in Łódź and, following a considerable success in elections, he won a seat in the Sejm, becoming Chairman of the Parliamentary Group of the Social Democracy of the Polish Republic. In three subsequent elections to the Sejm, he ran each time from Łódź, each time gaining more and more votes (from 50 thousand in 1991 up to 146 thousand in 2001); he held a seat in Parliament until 2005.