The merger will create the eighth largest bank in the US and a powerhouse in the country's north-east. However, the process of fusing the two banks will mean the loss of more than 4,500 jobs, partly because of the elimination of overlapping branches. The city of Boston will feel the brunt of the changes.
Analysts, many of whom had been predicting a sale of BankBoston, perhaps to a foreign bank, saw sense in the agreement.
"These banks should definitely do much better on a combined basis than stand-alone," commented Diana Yates of AG Edwards. "They don't have to compete with each other."
Fleet has grown quickly recently, acquiring, for example, the former US retail banking business of National Westminster. It also brings with it the discount brokerage Quick & Reilly.
BankBoston boasts a wide network of retail banks as well as the investment firm, BankBoston Robertson Stephens. It also has a big presence in Argentina and Brazil.
The deal, which is scheduled to close by year-end, is certain to come under the microscope of anti-trust watchdogs in Washington. To appease concern, the two banks are expected to shed some $13bn in customers' deposits.
The early response yesterday on Wall Street was lukewarm. Shares in Fleet were off slightly in morning trading while those in BankBoston were up only slightly. They remained well below the $53 share value put on the bank by the deal.