"I invite all parties to be part of a government of national unity," Sirisena said in his first address to the nation from the central town of Kandy after winning the historic elections that ended the 10-year rule of Mahinda Rajapaksa.
Sirisena said as pledged in his campaign manifesto, the powers of the executive president will be conferred to parliament.
Eliminating poverty would be the priority for his government, he said. He also promised to strengthen economy with friendly foreign policy.
"Its not a king we need in this country but a true servant of the people," Sirisena said in a obvious reference to his predecessor Rajapaksa, who was hailed a 'King' for his action to defeat the LTTE's separatist campaign.
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Sri Lanka's minorities include Tamils (13 per cent) and Muslims (17 per cent).
Rajapaksa's Health Minister until late November, Sirisena defected to become the opposition unity candidate in the January 8 polls.
He has appointed the main opposition leader Ranil Wickremesinghe as the new Prime Minister.