But Rajapaksa is short of votes in parliament to return to power as prime minister and the sacked, Western-friendly premier, Ranil Wickremesinghe, has refused to back down.
Wickremesinghe had late Thursday thanked his supporters in a Facebook video for not letting Sri Lanka be "plunged into the darkness of dictatorship".
It was not immediately clear how Sirisena can legally dissolve parliament, though his legal experts have said there are provisions for him to do so.
Sri Lankan President Maithripala Sirisena Friday dissolved parliament, paving the way for an early general election in the country which is grappling with unprecedented political crisis after the surprise sacking of Ranil Wickremesinghe as Prime Minister and replacing him with Mahinda Rajapaksa.
He said in a statement that a new parliament will be convened on January 17, after a general election is held on January 5.
Before he signed the papers dissolving parliament and calling the election, Sirisena appointed allies of his and of Rajapaksa to cabinet positions. Sirisena said he had to fire Wickremesinghe for mismanaging the economy and because of a Cabinet minister's alleged involvement in a plot to assassinate Sirisena.
Political parties representing a majority of members in the 225-member parliament closed ranks to denounce the Friday night dissolution as illegal and unconstitutional. "At the end of the day, he is a victim of his own homegrown crisis".
Amid the pressure, Sirisena announced the legislature would be summoned November 14.
The UNP is likely to contest the move because of constitutional provisions stating a parliament can not be dissolved until four and a half years after its inception.
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The incoming head of the House Foreign Affairs Committee warned Sirisena he was jeopardizing United States assistance including a package under discussion through the Millennium Challenge Cooperation, which supports countries that observe democratic norms. The current Parliament was elected in August 2015.
Sri Lanka's largest party vowed to mount a full scale challenge to the "tyrant" President Maithripala Sirisena after the shock sacking of parliament that left the country teetering on the edge of further civil unrest.
"This is a gross violation of the constitution", Harsha De Silva, a lawmaker in Wickremesinghe's party, said in reference to the dissolution of parliament.
"We will fight the emerging tyranny of Sirisena".
The admission, which came despite Sirisena's earlier claim that he had the support of 113 legislators when he sacked Wickremesinghe, had fuelled speculation that he would go for snap elections.
"As a committed partner of Sri Lanka, we believe democratic institutions and processes need to be respected to ensure stability and prosperity".
Rajapaksa indicated what was coming hours before the dissolution in a speech.
"We will show that we have the parliament majority and we will show that the dictator president has dissolved a government which had a majority in the parliament", he told reporters.