Płażyński began his political career in 1980 / 1981 as one of the leaders of the Students' Solidarity; he was governor of the Gdańsk Voivodship from August 1990 to July 1996, and was elected to the Sejm (the lower house of the Polish parliament) in September 1997. From 1997 to 2001, he also held the office of marshal of the Sejm, after being elected without a single vote against him.
In January 2001, he founded the political party Platforma Obywatelska together with Donald Tusk and Andrzej Olechowski. He left Platforma Obywatelska due to personal reasons and is now an independent MP.
Maciej Płażyński is married to Elzbieta Płażyńska and has three children: Jakub, Katarzyna and Kacper.