Deputy Prime Minister Michael is going to resign his position along with Prime Minister Helen Clark.
Dr Cullen, who as finance minister has been the most important politician after Helen Clark for the last nine years, said today it was time to move on as the Labour Party went through a rebuilding phase.
Helen Clark announced she was stepping down from the leadership in last night's concession speech.
"Helen Clark and I have worked very closely leading the team over the last 12 years, particularly the last nine years in government," he said in a statement.
"We are both proud of Labour's achievements in government. However, it is time to move on from a leadership position as the party rebuilds."
Dr Cullen said he wished Bill English well as the next minister of finance in troubled international economic times.
National Party leader John Key announced before the election that Mr English would be finance minister in his new government.
Dr Cullen said he looked forward over the next three years to seeing a big narrowing in the wage gap between Australia and New Zealand, significantly higher productivity, shorter hospital waiting lists, much reduced serious crime and improved education standards - all promises made by the National Party during the campaign.
"Labour will measure National in government against the commitments it has made and I will play my part in holding the National-led government to account as Labour rebuilds and prepared for the next general election," Dr Cullen said.
Dr Cullen is a list MP and could resign at any time without causing a by-election, but his comments appeared to indicate he will stay on for the three-year term of Parliament.
Helen Clark said last night she would remain as the MP for Mt Albert through the next parliamentary term.