He was elected to the Sejm in 2001 and reelected on 25 September 2005, receiving 31,253 votes in 33 Kielce district as a candidate on the Law and Justice list.
He was the majority leader between 3 November 2005 and 19 July 2006. He has been a minister (Chairman of the Standing Committee of the Council of Ministers) since 14 July 2006. On 8 May 2007 he became Deputy Prime Minister of Poland and held that position until 11 November 2007.
On 16 April 2010, Gosiewski was posthumously awarded the Commander's Cross with Star of the Order of Polonia Restituta and on 29 April 2010, the City Council in Ostrowiec made him an honorary citizen.