Murray McCully leaves New Zealand today on what is likely to be his last trip as Foreign Minister.
He's travelling to Vietnam for talks with President Tran Dai Quang and senior colleagues.
A new foreign minister is expected to be appointed in a Cabinet reshuffle to be announced tomorrow.
Mr McCully is New Zealand's third longest-serving foreign minister, behind Sir Keith Holyoake and Sir Don McKinnon.
Education Minister Hekia Parata is also expected to step down in the reshuffle.