Michael Cullen was born on 5 February 1945. He was born in the city of London, in the United Kingdom, but moved to New Zealand while young. He attended secondary school in Christchurch, and subsequently obtained an MA in History from Canterbury University. He then gained a PhD in Social and Economic History from Edinburgh University. From 1971 to 1981, he was a lecturer at Otago University (with a term as a Visiting Fellow at the Australian National University from 1975 to 1976).
Cullen joined the Labour Party in 1974, and served on the party's Executive and Council between 1976 and 1981. In 1981, he was elected MP for the electorate of St Kilda. When Labour entered government in 1984, Cullen became Senior Whip.
Due to his knowledge of economics, Cullen became increasingly involved in the disputes surrounding the Minister of Finance, Roger Douglas, who supported the liberalization of trade and the sale of state assets. These goals, which were against traditional Labour policies, angered both party members and the public. When the Prime Minister, David Lange, attempted to limit the influence Douglas had on the government's direction, Cullen became involved on Lange's side. After Labour's reelection in 1987, Cullen was made Associate Minister of Finance (an attempt by Lange to provide an anti-reform counterbalance to the radical Douglas) and Minister of Social Welfare (an attempt to limit the impact of the reforms in that area).
Eventually, Douglas was forced to resign, but a month later, the political controversies around the dispute prompted the resignation of Lange himself. Douglas was succeeded as Finance Minister by David Caygill, one of his allies (albeit a considerably less radical one). Cullen was made Associate Minister of Health, again to reduce the effect of reforms on that sector.
When Labour lost the 1990 elections (something attributed by many people to public anger at Douglas's reforms), Cullen returned to being Labour's spokesperson on social welfare. The following year, he replaced David Caygill as the party's chief finance spokesperson, although Caygill remained a deputy leader of the party. When Caygil retired from politics in 1996, Cullen took the deputy leader's post as well. Before Labour's position in the polls improved, Cullen also made an attempt to oust Helen Clark as party leader, but failed. The two do not appear to bear each other any resentment, however. Cullen claims to be happy with his position as second, saying that in terms of personality, he is "a number two sort of person". Many commentators agree, believing that Cullen's strength lies more in administration than leadership.
Labour's electoral victory in 1999 resulted in Cullen becoming Finance Minister. After the 2002 elections, it was decided that the size of Labour's junior coalition partner was not sufficient to justify its leader's high office, resulting in Jim Anderton stepping down as Deputy Prime Minister to make way for Michael Cullen.
When Cullen was first appointed Finance Minister, many parts of the business community were concerned that he would adopt a unrealistic positions driven by his political views. Slowly, however, the business world lost much of its fear of him, and most people now concede that he is a competent administrator (even if they disagree with the direction he selects). Cullen has also performed well against Don Brash, a former governor of the Reserve Bank who became the opposition National Party's finance spokesperson. He is considered to be one of the Labour Party's best debaters, and is known for his sometimes "acerbic" sense of humour.