COBA will commence a national search for a new chief executive immediately, overseen by the board.
COBA chair Don Magin said Ms Petschler had made a significant contribution to COBA and the sector, and she would be missed.
“The board acknowledges the outstanding contribution that Louise has made to COBA and the sector, and the many milestones that have been achieved under her leadership,” Mr Magin said.
“COBA has matured and grown significantly in performance, focus and influence,” he said.
“Louise’s passion for customer owned banking, and her commitment to a united industry ‘voice’ for the sector, have been key drivers in COBA’s work and success.”
Ms Petschler acknowledged the support of the board and members during her time as CEO and paid tribute to the professional COBA team.
“It has been my privilege to serve as COBA’s CEO. For a supporter of customer owned banking and its potential, there is no more challenging or rewarding role,” she said.
Ms Petschler will finish at COBA on August 8.
COBA head of public affairs Mark Degotardi will be acting CEO from August 9.