IMB Bank and Hunter United Employees Credit Union have completed their merger after receiving approval from APRA.
This was delayed by a month as APRA prioritised other work.
IMB chief executive Robert Ryan said in a statement that Hunter United, whose assets have been transferred to IMB, will operate under its own brand as a division of IMB.
Hunter United members will have access to a bigger range of products and services. The combined group will have greater scale for investment.
Current banking arrangements will remain in place while the two banking systems are integrated, which is expected to take about nine months.
IMB confirmed that there would be no job losses.
Hunter United has 10,000 members and A$355 million of assets. The combined group will have 207,000 members, $6.3 billion of assets, 53 branches and more than 600 employees.