She was the first permanent wheelchair user in the House of Commons since 1880.
Begg was educated at the Damacre Primary School (Brechin), Brechin High School and the University of Aberdeen where she earned an MA in History and Politics. From Aberdeen College of Education (now the Faculty of Education of the University of Aberdeen), she gained a Secondary Teaching Certificate in 1978.
From 1978, she taught history and English at the Webster's High School in Kirriemuir. She joined the Labour Party in 1983. In 1988, she became the principal teacher of English at the Arbroath Academy. In the same year she won the Disabled Scot of the Year Award.
Begg has been a wheelchair user since 1984 as she lives with the degenerative Gaucher's disease. She was the second full-time user of a wheelchair elected to the House of Commons, after Arthur MacMorrough Kavanagh who was first elected in 1868 and sat until 1880.
Begg was selected to stand for election for Labour through an all-women shortlist. and when Aberdeen South (like many seats) fell to Labour in their landslide victory at the 1997 general election. She defeated the Conservative Parliamentary Under Secretary of State at the Scottish Office Raymond Robertson. In 2001, she became the first Labour MP to retain the Aberdeen South seat.
She made her maiden speech on 21 May 1997. She was Secretary of the All-Party BBC Group and Chair of the All Party Group on Equalities, the All Party Oil and Gas Industry Group, the All Party Group on Chronic Pain, and the All Party Commercial Radio group. She was a member of the House of Commons Chairmen’s Panel and Vice Chair of the Speaker's Conference which was tasked with looking at the under representation of women, ethnic minorities and disabled people in the House of Commons. She chaired the Work and Pensions Select Committee from July 2010.
Begg lost her seat in the 2015 general election to Callum McCaig of the Scottish National Party.
Begg voted in favour of a bill that banned smoking in restaurants in April 2003. In December 2004 and October 2005, she voted in favour of the Identity Cards Bill. She voted in favour of allowing unmarried heterosexual and homosexual couples to adopt, and in favour of the Civil Partnership Bill.
In March 2002, she voted to ban the hunting of wild mammals with dogs. She voted in favour of the NHS Foundation Trust proposal and against the replacement of the Trident system.
She voted in favour of adding clauses to a bill that allow the Secretary of State to detain indefinitely, pending deportation, anyone he suspects is a terrorist, even if the law forbids that person's deportation from ever taking place. She voted against allowing people detained at a police station to be fingerprinted and searched for identifying birthmarks unless it is in connection with a terrorism investigation.
In March 2003, she voted against the declaration of war against Iraq.
In June 2003, she voted against a motion that would have recalled the Prime Minister's assertion that Iraq had weapons of mass destruction that could be used at 45 minutes' notice, and launching an independent inquiry into the intelligence received and the decisions that were based on it. In June 2007, she voted against a motion calling for an independent inquiry by a committee of Privy Counsellors into the Iraq War.
In November 2008, Begg was one of 18 MPs who signed a Commons motion backing a Team GB football team at the 2012 Olympics, saying football "should not be any different from other competing sports and our young talent should be allowed to show their skills on the world stage". The football governing bodies of Scotland, Wales and Northern Ireland are all opposed to a Great Britain team, fearing it would stop them competing as individual nations in future tournaments.
During the 2009 MPs expenses scandal, Begg was one of the first Scottish MPs to take the step of publishing all of her claims under the Additional Costs Allowance on her website before they were released by the House of Commons authorities saying that it was "important people can see how MPs spend taxpayers' money."
In June 2011, Begg crossed swords with Philip Davies, Conservative MP for Shipley, over the issue of disabled people being allowed to work for less than minimum wage if they so choose in order to establish themselves in employment. Davies explained that he was representing the views of constituents anxious to get a foothold on the earnings ladder, but Begg believed that this was simply an attempt to discriminate against disabled people.
Begg is a vocal campaigner for allowing embryonic stem cells to be used in the research for treatments of diseases, including currently incurable conditions such as Alzheimer's and Parkinson's Disease. She has also been heavily involved in lobbying the Department of Health against an all-out ban on the pain-relief drug co-proxamol, used by many people who suffer from chronic pain conditions.
She has also taken the lead in lobbying the government on issues such as the Seafarer's Earnings Deduction and compensation for trawlermen who lost their livelihoods during the Cod Wars. In the 2009 Budget, Begg also won a concession from the Chancellor of the Exchequer, Alistair Darling MP, that "those caring responsibilities of grandparents of working age will count towards their entitlement to the basic state pension." Begg had campaigned for grandparents of working age to receive National Insurance Credits in recognition of the fact that their caring role may impact on their contributions to their state pension entitlement.
On the floor of the House of Commons, Begg vehemently criticised fraudsters who take advantage of vulnerable people in her constituency through the use of mail scams and pyramid schemes.
Begg was one of the most vociferous critics of Aberdeen City Council during the budget crisis of 2008, which led to many of her constituents having their services cut. In 2009 she criticised as "draconian" a move by Aberdeen City Council to set a debt collection agency on an 80-year-old partially sighted woman for the sum of £17.50.
Begg also wrote to the Scottish First Minister Alex Salmond requesting a change to the house buying system in Scotland. She also criticised plans to close an Aberdeen school 18 months after it had been saved, saying that they were "closing the school by stealth."
In November 1999 Begg sustained a broken wrist and a broken leg and was knocked from her wheelchair in a road accident outside Aberdeen Airport. Begg was forced to stay in hospital for three months as a result of her injuries.
She was appointed Dame Commander of the Order of the British Empire (DBE) in the 2011 New Year Honours for services to disabled people and to equal opportunities.