Harvard Pilgrim Health Care and Tufts Health Plan, two of the region's largest insurers, announced Wednesday they had reached a definitive agreement to form a single company that would serve nearly 2.4 million subscribers in New England.
In a joint statement, the insurers said the merger would create one of the largest nonprofit health services organizations in the region.
The deal faces scrutiny from government regulators, including the Massachusetts Attorney General's office and the state Division of Insurance.
"Both organizations share the same vision that a combined organization will be even more effective, better able to keep high-quality health care accessible and affordable, while at the same time investing in programs and initiatives that enhance quality," the companies said.
Under the agreement, Tom Croswell, president and chief executive of Tufts Health Plan, would serve as CEO of the combined organization, which has yet to be renamed. Harvard Pilgrim's top executive, Michael Carson, would serve as president and oversee the company's various business lines and subsidiaries, according to the statement.
The current chair of Harvard Pilgrim's board of directors, Joyce Murphy, would serve as chair of a new board that would have equal representation from both companies.
Financial terms of the agreement were not disclosed.
Close to 2.4 million people in Massachusetts, Maine, Connecticut, New Hampshire and Rhode Island will be served by the new company, Harvard Pilgrim Health Care and Tufts Health Plan said.
Several units within the Massachusetts Attorney General's office, including the antitrust, public charities and health care divisions, could be involved in examining elements of the deal to weigh possible impacts on consumers and the health care market in general.
"Our office has been in touch with both parties and will review the proposed transaction as more information becomes available," said Meggie Quackenbush, a spokeswoman for Democratic Attorney General Maura Healey.
The merger "could have a significant impact on the Massachusetts health care market," said Matthew Kitsos, a spokesman for the Massachusetts Health Policy Commission, an agency that does not have regulatory powers but provides analysis of health care costs and benefits.
Kitsos said the commission was also looking forward to learning more details about the agreement.
The two companies explored a merger in 2011, but decided at that time to remain separate.