Eastern Bank was established on April 15, 1818 as Salem Savings Bank and became FDIC insured on October 1, 1983.[6] On October 19, 1989, Eastern Savings Bank's parent company Lynn, Massachusetts-based Eastern Bank Corporation, renamed it Eastern Bank, while also reorganizing it into a mutual holding company, making it the first of its kind in Massachusetts.[6][7]

In the years following its reorganization, it made several acquisitions of local banks. They included Shore Bank And Trust Company (Lynn, April 1992), Malden Trust Company (Malden, May 1992), First Colonial Bank For Savings (Lynn, October 1993), and Saugus Bank And Trust Company (Saugus, November 1994).[6]

Former MASSBANK location in Downtown Melrose. Divested after temporary rebranding. In 1997, Eastern began an aggressive expansion program with the aim of doubling its size within five years.[8] The first acquisition of the program was initiated in early 1998 when Eastern bought the ten branch Quincy-based Hibernia Savings Bank and its parent holding company Emerald Isle Bancorp, Inc for $80 million and converted all branches to Eastern Banks.[7][9] Eastern, with the bulk of its branches north of Boston, gained exposure to the market south of Boston through the acquisition. In November 2002, Eastern Bank merged its operations with its subsidiary, Salem-based Eastern Bank & Trust Company.[6] The following year in March 2003, company headquarters were moved from Lynn to Boston's Financial District, positioning it alongside the regional headquarters of other large banks including FleetBoston Financial and Citizens Bank.[6][8] Continually expanding its footprint in the region, Eastern purchased Wareham's Plymouth Savings Bank in May 2005 and Sharon Co-operative Bank in May 2007. Eastern Bank announced in March 2008 its intention to buy Reading-based MassBank Corp. for $170 million.[3][10] Eastern's third acquisition in the past four years, it doubled its deposits in Middlesex County to more than $1.4 billion, garnering a 4% market share in the county.[10] In late June 2010, it was announced that Eastern Bank was the winning bidder to acquire independent Massachusetts bank Wainwright and its 12 branches located in Boston and the surrounding communities. The bank, "known for its social activism and lending to nonprofit organizations", will be purchased for $163 million or $19 a share; almost double its $9.62 closing stock price prior to the announcement