Prime Minister Bill English said he was not surprised McCully had decided to move on in 2017 after eight years as Foreign Minister.
McCully announced today that he would not stand for Parliament in 2017. He had earlier ruled out standing in the East Coast Bays electorate, but said he would stay as long as then Prime Minister John Key wanted him in the Foreign Affairs portfolio.
Asked if McCully had left before he was pushed or if the reshuffle was a factor, English said he was not surprised McCully was going after a "fantastic run".
"There's no doubt the change in leadership has provided an opportunity - well, a catalyst - for people to decide what they are going to do.
"Murray has made a decision and let us know about it."
He said McCully's tenure had included dealing with tough issues on the Security Council over the past two years of New Zealand's membership.
"He's now one of the most experienced foreign ministers in the developed world."
He said he would wait until his reshuffle on Sunday to say whether McCully would stay on as Foreign Minister for a period of time or be replaced immediately.
McCully made the announcement from New York, where he is attending the Security Council and continuing to push for progress on Aleppo and the Middle East Peace Process. New Zealand's term on the Security Council ends at the end of this month.
In a statement, McCully said he would not put his name on the National Party list for 2017 and would bow out of politics at that point, but would stay on in Foreign Affairs until then if that was Prime Minister Bill English's wish.
"In light of the upcoming Cabinet reshuffle, I want to be clear that I will not be a nominee for the National Party list. I have made the Prime Minister and other senior colleagues aware of this position," McCully said.
"I feel greatly privileged to have had a unique partnership with John Key in managing New Zealand's foreign policy interests for over eight years," he said today.
McCully did not say whether he would stay until the 2017 election - that may depend on whether English wants him to remain in Foreign Affairs until that point. McCully said English had his complete support.
"I want to ensure that New Zealand's international relationships have a smooth transition from the Key Government to the English Government. How I might best contribute to that process is a matter for the Prime Minister."
"We can look back on some significant foreign policy achievements, including New Zealand's election to the United Nations Security Council, where I am currently attending my final meetings in New York prior to the conclusion of our term at the end of December."
Erica Stanford was selected as National's candidate in East Coast Bays last month.
Stanford is one of McCully's local electorate staffers but has worked overseas in export roles.