Demonstrators and government supporters clash outside the President's office in Colombo on Monday. AFP
Amarakeerthi Athukorala opened fire and critically wounded two people blocking his car in the town of Nittambuwa, police said, adding that one of the victims died of his injuries.
"The MP fled the scene and took refuge at a nearby building," a police official told AFP by telephone. "Thousands surrounded the building and he then took his own life with his revolver."
The incident came as thousands took to the streets across the curfew-bound island and targeted supporters of Prime Minister Mahinda Rajapaksa, who has subsequently tendered his resignation.
The Rajapaksa loyalists had earlier in the day destroyed tents and placards of anti-government demonstrators camping outside the official residence of President Gotabaya Rajapaksa since April 9.
In violence in the capital Colombo, at least 138 people were wounded and admitted to the Colombo National Hospital, a spokeswoman for the hospital said.