In 1994 Östros was elected to the Riksdag as a member of parliament. In 1996, he became the Minister for Taxation at the age of 31, under the Cabinet of Göran Persson, and later served as Minister for Education from 1998 to 2004. In 2004 he switched posts with Leif Pagrotsky and became Minister for Enterprise and Energy, a position he held on to until the Social Democratic defeat at the general elections of 2006. Östros was also the deputy chairman of the Riksdag's committee for Industry and Trade from 2006 to 2008.