Oliver H. Sommer’s departure from First Niagara Financial Group was a lucrative one.

The former executive will receive a gross payment of $871,250 as part of his severance package, First Niagara said in a regulatory filing.

The payment is equal to Sommer’s annual base salary at his June 28 effective date of termination, plus his 2013 targeted bonus amount, the Buffalo-based bank said. The severance payments will be made in biweekly increments of $33,509.

Sommer was the bank’s executive vice president of corporate development. He specialized in helping First Niagara identify and complete acquisitions. The bank has shifted toward running its operations rather than making more deals.

Sommer’s severance package also calls for him to receive a one-time cash lump sum of $10,000 for expenses related to his termination, including legal fees. He was due to receive that sum within 30 days of the agreement, which was effective July 17.

The agreement also says more than 25,000 shares of stock previously issued to Sommer were to become fully vested to him on the date the agreement took effect.

Another element of Sommer’s severance package involves his home. First Niagara will maintain the discounted interest rate on his home mortgage at the same rate in effect before his termination date, until the home is sold.

Sommer’s departure was announced shortly before the bank disclosed John R. Koelmel’s departure as chairman and chief executive officer. First Niagara officials recently said they are continuing their search for a permanent replacement for Koelmel.