"We made every important decisions today in achieving greater democracy, establish rule of law," said Anura Kumara Dissanayake, leader of the JVP or People's Liberation Front.
"We decided to present in parliament the 19th amendment aimed at abolishing executive presidency, establishing independent commissions," Dissanayake said.
Sri Lanka's new President Maithripala Sirisena had pledged greater democratic reforms in his election manifesto as the opposition unity candidate.
His 100-day programme envisages to slash the authoritarian powers of his predecessors.
Addressing a group of Buddhist monks, Prime Minister Ranil Wickremesinghe said that the government hopes to reach accord with other political parties on the constitutional reforms.
"We are working round the clock to achieve our 100 day programme so we need support from all parties," Wickremesinghe said.