He had been unable to connect with voters and Labour's share of the vote steadily declined, accelerated by his apology for "being a man".
"I know that I go out knowing I have done my best and having, I hope, made a difference," he said today.
"I have always said 'politics is not a job for life'.
"You do your very best to serve your country and then you think the time has come, you move on and that clears the way for other people, for younger people to come in and give of their best.
"That is how we refresh and that is how we serve."
AVOIDING BY-ELECTION
Cunliffe intends to step down next year, likely within six months of the next election to avoid triggering a by-election in his New Lynn electorate.
Cunliffe is taking up a role at the Auckland-based management consultancy Stakeholder Strategies Ltd.
He would not comment on the negative aspects of his leadership or accusations of disloyalty to former leader David Shearer.
"I'm feeling very positive about the next chapter in my life.
"They understand by the smile on my dial that I am going to a really good opportunity."
Cunliffe arrived in politics in 1999, the son of an Anglican vicar, with an impressive CV including a Harvard degree, a stint as a diplomat and experience with the Boston Consulting Group.
He became a minister after a term and eventually Helen Clark promoted him to the senior portfolio of Health in 2007 when he famously quipped to National Health spokesman Tony Ryall: "I'm running this show!"
Phil Goff took the leadership after the Clark Government was defeated in 2008.
Cunliffe first contested the leadership in 2011, which David Shearer won.
AGITATED FOR CHANGE
But Cunliffe's supporters and the party's ruling New Zealand Council were unhappy with the result and agitated to get the constitution changed to reduce the influence of the caucus in favour of party members and unions.
Once Shearer had been undermined sufficiently and resigned, Cunliffe won the leadership contest under the new rules.
Cunliffe said Andrew Little had his full support and he would make a fine Prime Minister
"The Labour Party is united, it is cohesive, it is determined to win. It is not about us. It is about the people we are here to serve."
Cunliffe's departure opens a chance for another MP in the historically safe Labour seat of New Lynn, although in 2014 Cunliffe's majority had dropped to 4557 and National beat Labour in the party vote.