"It has been a privilege to work alongside a talented team of fellow directors and senior managers to collectively guide its growth and development over this time".
He paid tribute to the two chief executives he has worked with during his chairmanship, Barbara Chapman and Vittoria Shortt. "I've been lucky to work alongside two very talented, capable and inspiring leaders."
Walker said he was delighted Dame Therese had agreed to take up the chairmanship role.
"Dame Therese has been an ASB director since 2015 and currently chairs the board audit and risk committee. She knows our business well and has strong governance experience, notably as the chairman of Air New Zealand. I will step away feeling very confident about the future direction of the bank."