Dugdale was born in Aberdeen on 28 August 1981. She attended secondary school at Harris Academy in Dundee, where she was Head Girl. She studied Law at the University of Aberdeen from 1999 until 2003, and completed a Master’s Degree in Policy Studies from 2004 until 2006 at the University of Edinburgh. Whilst attending university, she worked as Campaigns and Welfare Adviser for Edinburgh University Students’ Association and as Public Affairs Officer at the National Union of Students Scotland.

In the 2011 Scottish Parliament election, Dugdale was elected to the Scottish Parliament as Scottish Labour’s second candidate on their list for the Lothian region. She served as a Scottish Labour and Co-operative Party member and sat on the Local Government and Regeneration and Subordinate Legislation Committees. Dugdale was appointed as Scottish Labour’s Spokesperson for Education and Lifelong Learning on 29 June 2013.

Dugdale won the 2014 Scottish Labour Party deputy leadership election, succeeding Anas Sarwar, and defeating Katy Clark. As Scottish Labour leader Jim Murphy did not have a seat in the Scottish Parliament, she stood in for him at First Minister’s Questions. On 13 June 2015, she resigned from the deputy leadership in order to contest the 2015 Scottish Labour Party leadership election. She was succeeded by Alex Rowley after the leadership election.

During the 2015 leadership election campaign, Dugdale said she would want to end the charitable status of private schools in Scotland which gives them tax breaks, a policy in her opinion unfair to state schools. In a July 2015 televised leadership debate, she said it was wrong the vast majority of the 232 Labour MPs abstained on the Conservative government’s Welfare Reform and Work Bill in a second reading vote in the House of Commons. Following the resignation of Lord John Sewel on 28 July 2015, she said the House of Lords should no longer be an unelected chamber and should be moved to Glasgow. She won the leadership on 15 August, defeating Ken Macintosh.

Dugdale was Leader of the Scottish Labour Party during the 2017 general election. In the previous general election in 2015, the party lost 40 of its 41 seats in what was a landslide victory for the SNP, who won 56 of the 59 seats in Scotland. Nicola Sturgeon based the 2017 SNP campaign on a promise to seek a second Scottish independence referendum with the aim of keeping an independent Scotland inside the European Union, a referendum Ruth Davidson and the Scottish Conservatives were opposed to. Dugdale again campaigned on what she saw as the need for an income tax increase to tackle education underfunding by the SNP. The results gave Scottish Labour seven seats. In their previously sole seat Edinburgh South, Ian Murray was returned with a super-majority of over 15,000, and the party gained a further six seats from the SNP. However, the party came in third place behind the SNP with 35 seats and Scottish Conservatives with 13.

On 29 June 2016, Dugdale called for Jeremy Corbyn to resign from his position as Leader of the Labour Party, after 174-to-40 Labour MPs voted no-confidence in his leadership. She said when 80% of his own MPs no longer supported him, Corbyn could not properly function as Labour leader or Leader of the Opposition in parliament, nor could he form a potential alternative government. On 22 August, she declared her support for Owen Smith in the 2016 Labour Party leadership election but also said her position would remain tenable were Corbyn to win re-election. After Corbyn won the leadership election, she first said that this made the Labour Party unelectable, then stated the opposite.

In a 2016 interview with Mary Riddell for the Fabian Review, Dugdale said she was in a relationship with a woman but was disinclined to provide details of her private life. She first appeared in public with her partner Louise Riddell when they voted together in Edinburgh in the 2016 Scottish Parliament election. In February 2017, Dugdale revealed the couple had separated shortly after the New Year and following nine years together. In July 2017, it was reported Dugdale was in a relationship with Mid Fife and Glenrothes MSP Jenny Gilruth, a member of the SNP, and the two had started dating around four months earlier. In September 2017, she was named Politician of the Year at the Icon Awards, an awards ceremony celebrating Scotland’s LGBT community.

On 29 August 2017, Dugdale resigned as leader of Scottish Labour with immediate effect, commenting that it was time to “pass on the baton” to someone else. She opined that her successor needed the “space and time” to prepare for the next Scottish Parliament election in 2021.

In November 2017, ITV announced that Dugdale would appear as a contestant on its reality television series, I’m a Celebrity…Get Me Out of Here! It was subsequently reported that she faced disciplinary action from the Labour Party because she did not notify party managers she would be out of the country on non-work related business while the Scottish Parliament was in session. On 21 November, the party said that she would not be suspended. She subsequently received a written warning from Labour regarding the episode upon her return to Scotland in mid December.

In 2018, Stuart Campbell, a blogger running the pro-independence Wings Over Scotland website, started defamation proceedings against Dugdale about comments she made as a columnist for the Daily Record about his Twitter activity, a case he lost. The judgement said Dugdale was incorrect to imply Campbell had been homophobic but her article was protected under the principle of fair comment.

On 29 April 2019, Dugdale announced she would be resigning as an MSP before the summer recess of the Scottish Parliament in order to take up the role of director of the John Smith Centre for Public Service at the University of Glasgow. On 15 July 2019, Dugdale resigned as a Member of the Scottish Parliament. The following day it was announced she would be succeeded by former transport minister Sarah Boyack, who had been a candidate on the Lothian regional list in 2016. On 10 October 2019, it was revealed she had also resigned from Scottish Labour in the July, following disagreement with the party over Brexit.