However, the MP did not go without a fight.
Mr Benson-Pope (58) lost the Labour Party nomination for the electorate to Dunedin public relations consultant Clare Curran in a bitter battle that continues to split the electorate.
"I acknowledge the widely-held view that the candidate selection was not in the best interest of the electorate and that little regard has been given to the very high level of voter support that I have received in five terms as a [city] councillor and three terms as the parliamentary representative of this electorate," he said.
"In the end, however, I cannot respond to the disloyalty of a few by allowing any personal sense of betrayal to stand in the way of my political philosophy."
His decision not to stand came after a long and difficult consideration. He urged voters to cast their party vote for the Labour Party. He thanked all those who had offered support and asked him to stand.
Mr Benson-Pope will leave political life around the time of the November 8 election but he would not be drawn on his plans.
It was too soon to say, he said.
Of his 23-year career of public service in Dunedin, he said helping people with their issues was the best part of both jobs.
"I get a lot of phone calls about a lot of problems that are big for people in the community. We can deal with them through the office and my great staff in the office. That is the side of the coin many people don't see. They have no idea what an MP does during the day - or night."
Mr Benson-Pope also thanked the voters in Dunedin South for their support and advice during his time as their representative. It was a special honour and privilege to work with and to represent the residents of the electorate and a "very special" city, and to do that with such a consistently high level of community support.
"In my time as a city councillor and then MP we have together achieved a great deal. I know Dunedin will continue to go from strength to strength."
Among his personal highlights as a representative for Dunedin South were the $350,000 spent on resurfacing Bayfield Park, turning it from a mudbath into top playing fields when he was a councillor.
As an MP, he was particularly proud of the extra funding secured for Queens and Kings High Schools and the new gymnasium at Bayfield High School, where he once taught.
When he was first elected, he managed to convince Finance Minister Michael Cullen, the former Dunedin South MP, to increase the budget by $6 million so the historic Dunedin law courts could be refurbished.
Dunedin North MP Pete Hodgson said he was not surprised by Mr Benson-Pope's decision. The two met in 1976, when both were members of the Castle St branch of the party in Dunedin.
"It was clear to me long ago that his sense of loyalty to the party would mean he would not easily contemplate standing against it."