The mood of protesters was muted, with only around 100 people on the steps of the presidential secretariat. Many of the hundreds of thousands on the streets who forced the ouster of previous president Gotabaya Rajapaksa last week had wanted Wickremesinghe gone too, labelling him an ally of the Rajapaksa family.
"We're shocked. He's a person handling things in a very cunning way," protester Damitha Abeyrathne said of Wickremesinghe. "He will start controlling us in a different way. As protesters, we will start our struggle again."
"Unlike GR, Ranil is not a populist: he's known to be a ruthless pragmatist," Dedduwage said of Rajapaksa, using his initials.
The 225-member parliament gave 134 votes to Wickremesinghe and 82 to the other main candidate, ruling party lawmaker Dullas Alahapperuma. A third candidate, Anura Kumara Dissanayaka, got just three votes, according to the secretary general of parliament.
Wickremesinghe became acting president last week after Rajapaksa fled on a military plane to the Maldives and then took a commercial flight to Singapore.
"Now everyone must come together," the 73-year-old said after his victory.
"I accept the decision of parliament," he said. "My effort was to support consensus-based policy-making to provide solutions to a deeply suffering population. I believe the space for that still exists."