Her time as Northern Ireland Secretary saw the signing of the historic Good Friday Peace Agreement in 1998. Her personal charisma, reputation for plain speaking and successful fight against a brain tumour led her to be perceived by many as one of the most popular 'New' Labour politicians in the UK; a fact reflected in the standing ovation she received when Tony Blair mentioned her name in his speech at the 1998 Labour Party Conference.
She was a lecturer in the Political Science Department at the University of Wisconsin-Milwaukee in 1977, and at Florida State University (1977-1979). During her time in Tallahassee, she claimed that her apartment was broken into by Ted Bundy, a serial rapist who attacked several young women. She returned to England in 1979 to take up an apopintment at the University of Newcastle upon Tyne.
In 1981 she organised a series of alternative lectures — in parallel to the Reith lectures — which were published as Debate On Disarmament, jointly edited by Mowlam, with all proceeds from the book going to the Campaign for Nuclear Disarmament.
She was married to Jon Norton who was a banker in the City of London.
She had been a principal organiser, alongside Peter Kilfoyle, of Blair's campaign for the Labour leadership following the death of John Smith. As a member of Smith's shadow cabinet (Shadow Secretary of State for National Heritage) she had earlier courted controversy by calling for Buckingham Palace to be demolished (so antagonising monarchists) and replaced by a 'modern' palace built at public expense (so antagonising republicans). Later her willingness to speak her mind — often without regard to the consequences — was seen as her greatest strength by her supporters and her greatest weakness by critics.
She saw through the Good Friday Agreement signing in 1998, which led to the temporary establishment of a devolved power-sharing Northern Ireland Assembly. However, an increasingly difficult relationship with Unionist parties meant her role in the talks had been increasingly taken over by Tony Blair and his staff, prompting Mowlam to remark on one occasion (to Bill Clinton) "Didn't you know? I'm the new tea lady around here".
Whilst her deteriorating relationship with Unionists was the key reason she was replaced as Northern Ireland Secretary in October 1999 by Peter Mandelson, her move to the relatively lowly position of Cabinet Office Minister may have involved other factors, notably her health and her popularity. Mowlam had previously denounced the post as "Minister for the Today programme", and resented being appointed to it. As Cabinet Office Minister she was reportedly intended as Tony Blair's "Enforcer".
She was head of the Government's anti-drugs campaign, but undermined the campaign when she attracted media attention when in 2000 she admitted to using cannabis as a student. ("I tried dope. I didn't particularly like it. But unlike President Clinton, I did inhale")
In early 2000 she personally briefed the press that she was bored with her job and wanted to be Labour candidate for the post of Mayor of London. The stories were widely seen as damaging to Frank Dobson, the official Labour candidate, who was already facing serious difficulties in his campaign against Ken Livingstone, a popular but maverick politician who left Labour to stand as an independent for the post after his selection as official Labour candidate had been blocked. Mowlam's supporters briefed she was the only figure with sufficient popularity to challenge Livingstone, but the episode did nothing for either the Labour Party or Mowlam.
After retirement from the House of Commons she became a noted critic of government policy on various issues, especially foreign policy towards Iraq.
She continued public activity after retirement, becoming agony aunt for the men's magazine Zoo, saying that she missed her constituency work as an MP. She also set up a charity, MoMo Helps, to help drug users who are successfully completing their rehabilitation and provide support for the parents or carers of disabled children.
Her political memoirs, entitled Momentum, were published in 2002.
The BBC reported on 3 August 2005, that she was critically ill at King's College Hospital in London. She appeared to have suffered from balance problems as a result of her radiotherapy. She fell over, received head injuries and never regained consciousness. She had made a living will in which she had asked not to be resuscitated, and food and water were withdrawn.
On 12 August 2005, she was moved to Pilgrims Hospice in Canterbury, Kent where she died seven days later, aged 55, survived by her husband, Jon Norton, and two stepchildren. She died just 13 days after Robin Cook, another member of the 1997 New Labour Cabinet.
A Mo Mowlam memorial was held at The Theatre Royal, Drury Lane on 20 November 2005, and another in Redcar on 3 December.