Short was briefly married to fellow student at 18 after she had a child at 17. Their son was given up for adoption, and did not make contact with his birth mother until 1996. She discovered that her son was a staunch Conservative who worked in the financial sector in the City of London, and that she was a grandmother. Her second marriage, to former Labour minister Alex Lyon, turned to tragedy: he suffered from Alzheimer's disease and died in 1993. Short is a cousin of Canadian-American actor/comic Martin Short (their fathers were brothers) and of the Irish Minister for foreign affairs Dermot Ahern. Her uncle, Patrick Short, was known as the proprietor of Shorts Bar, a Republican hangout in South Armagh.
With a degree in political science from the University of Leeds, to which she transferred from Keele, she became a civil servant in the Home Office. Working as Private Secretary to the Conservative minister Mark Carlisle gave her the idea that she "could do better" than many of the MPs she dealt with, and in the 1983 UK general election she became MP for Ladywood, Birmingham, the area where she grew up.
In 1986 she gained attention for campaigning against "Page Three" photographs of topless models in The Sun and other British tabloid newspapers. For this she was denounced by such papers as a "killjoy" and one of them bought and published photographs of Short in her nightwear from her first husband.
She supported John Prescott in the Labour deputy-leadership election in 1988 (against Eric Heffer and the incumbent Roy Hattersley), leaving the Socialist Campaign Group, along with Margaret Beckett, as a result of Tony Benn's decision to challenge Neil Kinnock for the leadership. She supported Margaret Beckett for the Labour leadership in 1994 against Tony Blair and John Prescott. She also called for the withdrawal of British troops from Northern Ireland.
She rose through the ranks of the Labour Front Bench, despite twice resigning from it - over the Prevention of Terrorism Act in 1988, and over the Gulf War in 1990. She became Shadow Minister for Women, and then Shadow Transport Secretary. At the 1995 Labour conference, Short denounced Liz Davies as "unsuitable" after Davies had been selected as a Parliamentary candidate by a constituency Labour Party in Leeds North-East. This was seen as an attempt to win the favour of the right of the party, especially Tony Blair. However, in 1996, Short was moved to the Overseas Development portfolio, a move which she saw as a demotion. She has been a controversial figure throughout her career, most notably when she called for the legalisation of cannabis.
On her appointment to the DfID, journalists asked Short whether she would be "good" (in other words, not cause embarrassment to the government). She replied "I'm going to try to be good but I can't help it, I have to be me". A few months later, the island of Montserrat (one of the United Kingdom's few remaining overseas territories) was devastated by a volcano eruption which rendered half the island uninhabitable; when the islanders asked for more help from the DfID, Short was reported to have remarked "they will be asking for golden elephants next", and refused to visit the island. This remark caused great offence to the Montserratians and others; Labour MP Bernie Grant said that "She sounds like a mouthpiece for an old 19th century colonial and Conservative government".
On 6 November 1997 Short sent a letter to Kumbirai Kangai, Minister of Agriculture in Zimbabwe, in which she stated that "we do not accept that Britain has a special responsibility to meet the costs of land purchase in Zimbabwe". She went on to write "We are a new government from diverse backgrounds, without links to former colonial interests. My own origins are Irish and, as you know, we were colonised, not colonisers." In the same letter she did, however, offer qualified support for land reform: "We do recognise the very real issues you face over land reform... we would be prepared to support a programme of land reform that was part of a poverty eradication strategy, but not on any other basis". This letter caused a rift with the Zimbabwean government, which asserted that the Lancaster House Agreement of 1979 had contained a continuing pledge from the United Kingdom government to assist in land reform.
In December 1997, Short signed the U.K. into the Ottawa Convention, banning the production, handling and use of anti-personnel mines.
Short remained in the Cabinet for two months after her decision to back the 2003 Iraq War. She resigned on 12 May.
A few days later (on 29 February 2004) Short appeared on ITV's Jonathan Dimbleby programme. She revealed that she had been written to by Britain's senior civil servant, Cabinet Secretary Andrew Turnbull. Turnbull's confidential letter (which Short showed to Dimbleby, and which was quoted on the programme) formally admonished her for discussing intelligence matters in the media, and threatened "further action" if she did not desist from giving interviews on the issue. Turnbull wrote that she had made claims "which damage the interests of the United Kingdom", and that he was "extremely disappointed". The "further action" referred to in the letter has been interpreted as threatening either the removal of Short's status as a Privy Counsellor or to legal action under the Official Secrets Act. Either course of action would be without recent precedent; the last time a Privy Counsellor's status was revoked was in 1921 when Sir Edgar Speyer was accused of collaborating with the Germans during the First World War. However, on 1 March 2004, Tony Blair's official spokesman refused to rule out such a step.
However in the same interview on the Jonathan Dimbleby programme, Short backtracked on her claim about British agents bugging Annan. She admitted that the transcripts she saw of Annan's private conversations might have related to Africa and not to Iraq. Asked whether she could confirm that the transcripts related to Iraq, she said: "I can't, but there might well have been ... I cannot remember a specific transcript in relation, it doesn't mean it wasn't there." Short also admitted that her original claim, on the Today programme, that Britain had eavesdropped on Annan may have been inaccurate. Asked whether the material could have passed to the British by the Americans, she said: "It could. But it normally indicates that. But I can't remember that."
Clare Short's book, An Honourable Deception?: New Labour, Iraq, and the Misuse of Power, was released on 1 November 2004. It is an account of her career in New Labour, most notably her relationship with Tony Blair, the relationship between Blair and Gordon Brown and the build up to the 2003 invasion of Iraq.
In December 2004, Short was reportedly critical of U.S. efforts to dispense aid to countries devastated by a tsunami caused by a massive earthquake in the Indian Ocean. She was quoted as stating that the formation of a group of countries led by the United States for this purpose was a challenge to the role of the United Nations, which she believed was uniquely qualified for the task.
After Gordon Brown succeeded Tony Blair as Prime Minister, Short said that the change offered "a new beginning", and hinted that she might re-join the parliamentary Labour party if Brown changed the policies that had caused her to leave.
On 21 May 2008, Short gave a lecture as part of the Ebor Lectures 2008 Series on entitled "Apocalypse Now – Global Equity and Sustainable Living, the Preconditions for Human Survival." The lecture took place at York Minster and Short was introduced by the Dean of York, the Very Revd. Keith Jones.
In her lecture, Short emphasised the need for the end of our current 'throw away' society. She considered the changing conception of the world since the 1960s and emphasised the need for us to consider the consequences of today's environmental concerns for the generations of the future. Short also introduced the subject of Transition Towns, speaking about the first of such towns in Totnes, Devon, UK. These towns aim to create a "community" for the future which "addresses the twin challenges of diminishing oil and gas supplies and climate change, and creates the kind of community that we would all want to be part of. Short was particularly excited about the prospect of a Transition Town movement in Birmingham where her constituency is located.