Kevin Hague has become the first Green Party candidate to announce he wants to replace Russel Norman as the party's co-leader.
Dr Norman is stepping down at the Greens' annual meeting at the end of May.
Mr Hague said it is a crucial time for the party and he has the leadership skills the party needs and a strong track record of leadership in the community.
He said New Zealand needs the Green Party's values and policies more than ever.