The Pattali Makkal Katchi, a constituent of the Dravida Munnetra Kazhagam-led Progressive Alliance, will participate in the Congress-led coalition government at the Centre.
PMK founder S Ramadoss said at Tindivanam, Tamil Nadu, that he had taken the decision after considering the views of his party members.
The PMK won six Lok Sabha seats in Tamil Nadu and Pondicherry.
Ramadoss will leave for New Delhi on Sunday evening to meet Congress president Sonia Gandhi.
He is also expected to hand over a letter extending support to Gandhi to be forwarded to the President A P J Abdul Kalam.
PMK had participated in the government of outgoing Prime Minister Atal Bihari Vajpayee.