It said this is "to enable certain shareholder interest to be represented on the board of the bank.
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Analyst says de Mel, Welikala and Wijeyesinghe are making way to accommodate new members to the board nominated by the government.
The government now controls 25 percent of NDB Bank through holdings of state banks, insurance and pension funds.
This week state funds also bought into Hatton National Bank, a large listed commercial bank, raising their stake to about 25 percent.
The stakes were bought by the Employees Provident Fund, Sri Lanka Insurance Corporation, Bank of Ceylon and National Savings Bank.
National Development Bank said in a statement Russell de Mel assumed duties Friday, taking over from Eran Wickramaratne.
"NDB Bank has taken appropriate measures to ensure that the transition of the CEO would take place in a smooth and secure manner, while continuing to maintain its position as a solid financial conglomerate," it said.
Wickramaratne has been nominated by the