He said his stepping down was not related to his medical leave late last year.
"It is a real privilege to serve as Minister of Foreign Affairs. But it is an office that does not always sit easily with the role of a constituency MP."
Mr McCully regained his ministerial warrant in January after two-and-a-half months off work including a spell in North Shore Hospital's intensive care unit and contracting a superbug.
He had private surgery in November to remove a tumour from his pancreas, which turned out to be benign. He was rushed to North Shore hospital in an ambulance a week later when he contracted an infection and was admitted to the ICU. He then contracted the potentially deadly MRSA superbug.
Further infections about a week later were administered under a third general anesthetic.
Mr McCully has had a punishing travel schedule in the past few years, particularly campaigning successfully for a seat on the Security Council.
Murray McCully
• Has been an MP since 1987.
• A lawyer, he served in cabinet in the Bolger-Shipley administrations, and in the Key Government.
• He has attracted his share of controversy and survived some political scrapes, most recently the row over the Saudi sheep deal.
• In the 2015 New Year honours he was made a Companion of the New Zealand Order of Merit for service to foreign policy.
