The deal adds 176,000 customers with 4.84 billion euros in customer assets to Nordea's banking base and, in turn, allows Gjensidige to expand in its core market as the agreement will also see Nordea distribute Gjensidige's insurance products to its own 900,000 customers in Norway.

Like other banks, Nordea has been looking at online banking services to capture new customers that are increasingly logging online to shop and carry out other banking transactions. It recently began partnering with Apple Pay in Norway.

The purchase of Gjensidige Bank, one of Norway's leading online banks, is in line with this strategy. Nordea will take over Gjensidige's online network for selling digital banking services, mortgages, car financing, unsecured loans and savings and investments.

"We view Nordea and Gjensidige as natural strategic partners ... We are certain that the customers we both serve will benefit from the wider and better offering that will follow when the two strong partners join forces," Nordea Norway branch manager Snorre Storset said in a statement.

Nordea, which will move its headquarters from Sweden to Finland this year, said the deal was expected to boost its earnings per share from the first year.

The deal will also help it deliver annualised cost synergies of about 25 million euros ($29 million) by 2022 and generate a return on investment of about 16 percent.

Separately, Gjensidige, Norway's biggest insurer, said it expected to record a gain of about 1.9 billion crowns upon closing of the transaction.

The deal is expected to close in the first quarter of 2019. ($1 = 8.1717 Norwegian crowns) ($1 = 0.8584 euros) (Reporting by Ismail Shakil in Bengaluru and Esha Vaish in Stockholm; Editing by Gopakumar Warrier and Kirsten Donovan)