Dissanayake, whose leftist coalition won a record 159 seats in the 225-member parliament in a general election last week, also reappointed veteran legislator Vijitha Herath to helm the foreign affairs ministry.
Dissanayake, who has held the key finance minister portfolio since he was elected in September, would continue in that role, two party sources told Reuters on Monday, as Sri Lanka looks to chart a stronger recovery out of its worst financial crisis since independence from the British in 1948.
Harini Amarasuriya stays as Sri Lankan prime minister following the nation's parliamentary election. (EPA PHOTO)
A delegation from the International Monetary Fund (IMF) is in Colombo for a third review of its $US2.9 billion ($A4.5 billion) program that is expected to release a tranche of about $US337 million.
The new parliament will meet on Thursday to elect a Speaker and Dissanayake will present his key policy priorities to the newly minted MPs.
"This power comes with accountability. Accountability to the people, and this power should be wielded with humility, restraint and boundaries. I have every confidence in this cabinet and parliament," Dissanayake said in a speech after the swearing-in on Monday.
"The real work we will be judged on begins now."
A nation of 22 million, Sri Lanka was crushed by a 2022 economic crisis triggered by a severe shortage of foreign currency that pushed it into a sovereign default and caused its economy to shrink by 7.3 per cent in 2022 and 2.3 per cent last year.
The president will have to present an interim budget in the next few weeks, as well as find ways to reduce taxes and increase welfare, which were his key election pledges, without derailing the IMF programme.
Dissanayake will also have to complete a $US12.5 billion debt restructuring with bondholders and put growth on a sustainable path.
A political outsider in a country dominated by family parties for decades, Dissanayake comfortably won the island's presidential election in September.
But his Marxist-leaning National People's Power coalition had just three seats in parliament, prompting him to dissolve it and seek a fresh mandate in last Thursday's snap election.
Prime Minister Amarasuriya, 54, polled the second highest number of preferential votes and is an academic with a doctorate in social anthropology from the University of Edinburgh.
She will also hold the education and higher education portfolios.
