Duncan was born in Rickmansworth, Hertfordshire, the son of J.G. Duncan OBE, an RAF wing commander, and his wife Anne Duncan (née Carter), a teacher. The family travelled much, following Alan's father on NATO postings, including in Gibraltar, Italy, and Norway.

Alan Duncan was educated at two independent schools: at Beechwood Park School in Markyate, and Merchant Taylors' School in Northwood, at both of which he was 'Head Monitor' (head boy). Whilst coming from a Liberal family, and running (and losing) as a Liberal at a school mock election in 1970, Duncan joined the Young Conservatives in 1972. Alan Duncan had two brothers, who also attended Beechwood Park School, Robin and Kevin. Robin was also Head Boy.

Duncan then attended St John's College at the University of Oxford, where he coxed the college first eight, and was elected President of the Oxford Union in 1979. Whilst there, he formed a friendship with Benazir Bhutto, and ran her successful campaign to become the President of the Oxford Union. He then went on to win a Kennedy Scholarship to study at Harvard University between 1981 and 1982.

Upon graduation from Oxford, he worked as a trader of oil and refined products, first with Royal Dutch Shell (1979—1981) and from 1982 to 1988 for Marc Rich, working in London and Singapore. From 1988 to 1992, Duncan was self-employed, acting as a consultant and adviser to foreign governments on oil supplies, shipping and refining. In 1989, Duncan set up the independent Harcourt Consultants, which advises on oil and gas matters. He made over a million pounds after profiting from the need to supply oil to Pakistan after Kuwait's supplies had been disrupted in the Gulf War.

He has maintained his connections with the energy industry as a MP. He declares that he still owns Harcourt Consultants. In 2008 it emerged that Mr Duncan’s private office was being funded by donations from the chairman of Vitol while Duncan was shadow business secretary with responsibility for Conservative energy policy. He later declared the funding in the register of MPs’ interests.

Duncan was an active member of the Battersea Conservative Association from 1979 until 1984, when he moved to live in Singapore, from which he returned in 1986. After Prime Minister Margaret Thatcher resigned in November 1990, he offered his home in Westminster as the headquarters of John Major's leadership campaign.

Member of Parliament

Duncan first stood for Parliament as a Conservative candidate in the 1987 general election, unsuccessfully contesting the safe Labour seat of Barnsley West and Penistone. For the 1992 general election he was selected as the Conservative candidate for Rutland and Melton, a safe Conservative seat, which he won with 59% of the vote. In the Labour landslide of 1997 his share of the vote was cut back to 45.8% but has since increased to 48.1% in 2001 and 51.2% in 2005.

From 1993 to 1995, Duncan sat on the Social Security Select Committee. His first governmental position was as Parliamentary Private Secretary to the Minister of Health, a position he obtained in December 1993. He resigned from the position within a month after it emerged that he had used the right-to-buy programme to make profits on property deals. It emerged that he had lent his elderly next door neighbour money to buy his home under the right-to-buy legislation. The neighbour bought the 18th century council house at a significant discount and sold it to Duncan just over three years later. Gyles Brandreth describes this event in his diary as '...little Alan Duncan has fallen on his sword. He did it swiftly and with good grace.'

After returning to the backbenches, he became Chairman of the Conservative Backbenches Constitutional Affairs Committee. He returned to government in July 1995, when he was appointed Parliamentary Private Secretary to the Chairman of the Conservative Party, Brian Mawhinney. In November 1995, Duncan performed a citizen's arrest on an Asylum Bill protester who threw paint and flour at Mawhinney on College Green.

Duncan was a key player in the 1997 leadership contest, being the right-hand man of William Hague, the eventual winner. In this capacity, he was called 'the closest thing [the Conservatives] have to Peter Mandelson'. Duncan and Hague had been at Oxford at the same time, both been Presidents of the Oxford Union, and had been close, both politically and personally, since at least the early 1980s.

Front bench career

As a reward for his loyalty to Hague during the leadership contest, in June 1997, Duncan was entrusted with the positions of Vice Chairman of the Conservative Party and Parliamentary Political Secretary to the Party Leader. In June 1998 he became Shadow Health Minister. In June 1999 he was made Shadow Trade and Industry spokesman. In September 2001 he was appointed a Front Bench Spokesman on Foreign and Commonwealth Affairs.

When Michael Howard became Conservative party leader in November 2003, Duncan became Shadow Secretary of State for Constitutional Affairs, but as Howard had significantly reduced the size of the Shadow Cabinet, Duncan was not promoted to the top table. This continued to be the case when he was moved to become Shadow Secretary of State for International Development in September 2004. However, following the 2005 general election, the Shadow Cabinet was expanded to its original size once more, and Duncan joined it as Shadow Secretary of State for Transport.

He held this position for just seven months, becoming Shadow Secretary of State for Trade and Industry on 7 December 2005, after David Cameron's election to the party leadership the previous day. On 2 July 2007, he was appointed Shadow Secretary of State for Business, Enterprise and Regulatory Reform, as new prime minister Gordon Brown had abolished the Department of Trade and Industry the previous week, replacing it with the aforementioned new department. In January 2009 he became Shadow Leader of the House of Commons.

Failed leadership bid

Before the 2005 general election, Duncan was rumoured to be planning a leadership campaign in the event that then-leader Michael Howard stepped down after a (then-likely and later actual) election defeat. On 10 June 2005, Duncan publicly declared his intention of standing in the 2005 leadership election. However, on 18 July 2005, he withdrew from the race, admitting in The Guardian that his withdrawal was due to a lack of 'active lieutenants', and urged the party to abandon those that he dubbed the 'Tory Taliban':

Comments on Miss California Carrie Prejean

On the 24 April 2009 edition of television programme Have I Got News For You, Duncan was asked his opinion of Miss California USA 2009 Carrie Prejean publicly opposing same-sex marriage during the 2009 Miss USA pageant. Duncan replied, "If you read that Miss California has been murdered, you will know it was me, won't you?"

According to the Daily Mail, The Metropolitan Police received a complaint regarding the comment from George Hargreaves, leader of the small evangelical Christian Party whose members believe that homosexuality is a sin. According to Hargreaves, "Mr Duncan has crossed the line. A senior politician suggesting, even as a joke, that it is okay that Miss Prejean should be murdered for her evangelical Christian views is totally unacceptable." The BBC also reported receiving an unspecified number of complaints. In a statement published on 1 May 2009, the BBC stated:

We've received some complaints from viewers who were unhappy with Alan Duncan's comments about Miss California on Have I Got News For You, BBC One, Friday 24 April 2009.

Alan was not seriously suggesting Miss California should be killed. He was expressing his opinion on her views on gay marriage forcefully and in an exaggerated way for comic effect.

Duncan later remarked: "I'm sure [Prejean is] very beautiful and that if we were to meet we would love each other. I have no plans to kill her. I'll send her a box of chocolates — unpoisoned."

MPs' expenses 2009

As part of the British Parliamentary expenses scandal, the Daily Telegraph reported that Duncan allegedly claimed more than £4,000 over a three year period in expenses for gardening costs until he agreed with the Commons Fees Office that such claims "could be considered excessive" and stopped. Duncan quickly responded by suggesting that the reports in the Telegraph were "misleading", and that all his claims were "legitimate and approved by the fees office".

On 15 May 2009, the satirical BBC programme Have I Got News For You showed footage of Duncan's previous appearance on the show in which he boasted about his second home allowance, denied that he should pay any of the money back and stated it was "a great system". The show then cut to footage of David Cameron announcing that Duncan would return money to the fees office, followed by Duncan's personal apology, in which he called for the system to be changed.

Pranksters from online magazine and marketing company Don't Panic paid a visit to his constituency home where they planted flowers in the shape of a pound sign on his lawn and left a money tree. On 14 August, Duncan said (whilst being filmed without his knowledge by Don't Panic), that MPs, who are paid around £64,000 a year — within the top four percent of the population — were having, "to live on rations and are treated like shit. I spend my money on my garden and claim a tiny fraction on what is proper. And I could claim the whole lot, but I don't." These remarks attracted the attention of the press, and were criticised by commentators from all sides. Duncan apologised once more, and Cameron, though critical of Duncan's comments, denied that he would sack him from the Shadow Cabinet. Despite these assurances, on 7 September 2009, Duncan was "demoted" from the Shadow Cabinet, to become Shadow Minister for Prisons, after he and Cameron came to an agreement that his position was untenable.

Duncan is a libertarian. The Guardian has variously described him as 'economically libertarian' and 'socially libertarian'. He has been described as the 'liberal, urbane face of the Conservative Party'. He is a moderniser within the Conservative Party.

One of the chapters in his book Saturn's Children is devoted to an explanation of his support for the legalisation of all drugs. However this chapter was removed when the paperback edition was published to prevent embarrassment to the Party leadership. The omitted chapter is available on Duncan's personal website. He believes in minimising the size of government, and in Saturn’s Children advocated limiting government responsibility to essential services such as defence, policing and health. He has been described as a "staunch" Eurosceptic.

He is on the council of the Conservative Way Forward (CWF) group. He is one of the leading British members of Le Cercle, a secretive foreign policy discussion forum. In contrast with most members of both CWF and Le Cercle, who hold pro-Republican Atlanticist views, he actively supported John Kerry in the United States' 2004 presidential election. Duncan is friends with Kerry, having met him whilst at Harvard.

Duncan was the first sitting Conservative MP voluntarily to acknowledge that he is gay; he did this in an interview with The Times on 29 July 2002, although he has said that this came as no surprise to friends. Indeed, in an editorial published on the news of Duncan's coming out, The Daily Telegraph reported, "The news that Alan Duncan is gay will come as a surprise only to those who have never met him. The bantam Tory frontbencher can hardly be accused of having hidden his homosexuality."

On 3 March 2008 it was announced in the Court & Social page of The Daily Telegraph that Duncan would be entering into a civil partnership with his partner James Dunseath, which would make him the first member of either the Cabinet or the Shadow Cabinet to enter into a civil partnership. The two were joined as civil partners on 24 July 2008.

Duncan has a committed following in the gay community and is active in speaking up for gay rights. He was responsible for formulating the Conservatives' policy response to the introduction of civil partnership legislation in 2004, which he considered his proudest achievement of the Parliament between 2001 and 2005. In 2007, Pink News named him the 15th-most powerful LGBT person in the UK.

In April 2009, during the storm over Tony McNulty's second home allowance claims, he was reported to be one of sixty-five MPs to claim an expense on second homes whilst simultaneously receiving rental income from privately renting out other properties. Since 2001, he had claimed a total of £143,392 in second home allowance, despite owning two properties in Westminster, one of which he rents out. Reacting to McNulty's expenses claims, he has argued for the abolition of the allowance, in conjunction with an increase in MPs' salaries.

Books

He has written two books: An End To Illusions (Demos, 1993) ISBN 1-898309-05-1,and How the State Devours Liberty, Prosperity and Virtue[with Dominic Hobson], (Sinclair-Stevenson, 1995) ISBN 1-85619-605-4.The latter book presents a detailed case regarding the history and consequences of government control over institutions and activities which were historically private, to the extent that many citizens assume that privately or communally developed municipal facilities and universities are creations of the state, and that prohibitions on drug use, sex, and personal defence have always existed.

Television

He has appeared four times on the satirical news quiz Have I Got News For You: first appearing on 28 October 2005,then 20 October 2006,and again on 2 May 2008and 24 April 2009.His 2009 appearance sparked some controversy due to a badly received ironic joke about murdering the latest Miss California, who stated that she opposed same-sex marriages.