He was elected to the Sejm on 25 September 2005, gaining 20,741 votes in 1 Legnica district as a candidate from the SLD list.

On a national SLD convention in December 2009 he was chosen as the party's candidate in the 2010 presidential elections in Poland.

Szmajdziński died on the day after his 58th birthday, in the plane crash that also involved President Lech Kaczyński and 94 others.

[7] On 16 April 2010 he was posthumously decorated with the Commander's Cross with Star of the Order of Polonia Restituta.

On 20 May 2010 Wrocław city council granted him the title of Honorary Citizen of Wrocław and on 28 March 2011 Legnica City Council gave him the title of Honorary Citizen of Legnica.