He had previously survived an assassination attempt by the Tamil Tigers when he represented the United National Party, now the main opposition.
The politician ran a business which provided shipping services to the northern Jaffna peninsula.
The Tigers control the land route north to Jaffna on which they taxed goods and people, until the sea route was re-started by the government.
Most goods are now sent to Jaffna by sea using several vessels, some of which Maheshwaran operated.
But he had also been critical of the government's military campaign and allegations of human rights abuses by security forces and large scale arrests of Tamils.
The shooting took place as Maheshwaran attended a new year service in a Hindu temple in Kotahena, a northern suburb of the capital Colombo, with a high concentration of minority Tami