Mahinda Rajapaksa's party is hoping to secure a "super majority"
Sri Lankan President Gotabaya Rajapaksa has declared victory in the country's parliamentary election.
His brother Mahinda Rajapaksa is expected to be installed as prime minister, having held the role as caretaker since November.
The brothers' party, Sri Lanka People's Front, has secured a two-thirds "super majority" of seats needed to carry out its promised constitutional changes.
The party won 145 of the 225 seats, plus five more seats from its allies.
Mahinda Rajapaksa earlier tweeted that Indian Prime Minister Narendra Modi had called to congratulate him.
President Gotabaya Rajapaksa has been credited with helping contain the country's coronavirus outbreak
The controversial Rajapaksa family has dominated Sri Lankan politics for two decades. Mahinda Rajapaksa was previously president, from 2005 to 2015.
The opposition of former prime minister Ranil Wickremesinghe has been trounced, having lost all but one of the 106 seats it held in the outgoing parliament.
The main opposition party is now a new group established by the son of Ranasinghe Premadasa, a former president who was assassinated in 1993.
Sri Lanka has been one of the few nations to hold an election despite the coronavirus pandemic. The vote had already been postponed twice because of the virus.
The country has had relatively few confirmed infections and deaths of coronavirus - with a total of 2,839 cases and 11 deaths.
Another victory for controversial brothers
By Anbarasan Ethirajan, BBC South Asia Analyst
Once again it's a huge victory for the Rajapaksa brothers.
Just nine months after his impressive win in the presidential election, Gotabaya Rajapaksa has led his Sri Lanka People's Front to a two-thirds majority.
He is hugely popular among the Sinhala majority for crushing the Tamil Tiger separatist rebels in 2009 when he was defence secretary. Many in the country also credit his administration for bringing stability and successfully containing the coronavirus outbreak.
Gotabaya Rajapaksa is accused of human rights abuses during the civil war and also of targeting those who dissented. He always dismissed such accusations - but they have not gone away.
A surge in Sinhala nationalism in the run-up to the election has also worried Sri Lanka's minority communities.
Muslim leaders say their community is still reeling from the vilification that followed the devastating Easter Sunday suicide attacks by Islamist militants last year, which killed more than 260 people.
With their dominant majority, the Rajapaksas could attempt to change the constitution, increase the powers of the president so reversing the work of the previous government to introduce more checks and balances.
Activists, already alarmed by the diminishing space for dissent and criticism, fear such an eventuality could lead to ever greater authoritarianism.