Auckland Transport chief executive Shane Ellison has resigned and will leave the job in June next year.
Ellison began as chief executive of the council-controlled organisation in December 2017.
"It is the right time for the board to consider new leadership for a new phase at AT," he said in a statement.
"The organisation has many opportunities and challenges ahead as it continues to improve road safety, support mode shift, and responds to the climate crisis.
"The past four years have been very rewarding, with significant changes and many challenges, and I look forward to what is next for AT."
AT board chair Adrienne Young-Cooper said Ellison's leadership had brought significant cultural change within the organisation that will continue to be felt long after June 2022.
This has led to significant improvements in AT's performance, she said.
"Shane's work to change our focus from moving vehicles to moving people and freight will have lasting impacts both within AT and across the region.
"I thank Shane, on behalf of our board, for his service to Tāmaki Makaurau and wish him the very best."
Recruitment processes for a new chief executive are under way, and the AT board anticipates it will make an appointment ahead of Ellison's departure in June 2022.