Forbes was born in Dingwall in Ross and Cromarty in northern Scotland. Growing up, she spent three years in India, then was taught in a Scottish Gaelic school. She returned to India at the age of 10 and lived there until she was 15, with her father involved in providing healthcare to people who could not afford it. She returned to Glasgow, Scotland and finished her schooling at Dingwall Academy. She read history at Selwyn College, Cambridge, graduating with a BA in 2011. She worked as an accountant. She then studied at the University of Edinburgh, gaining an MSc in Diaspora and Migration History in 2013.
Political career
In August 2015, Forbes was selected from an all-women shortlist by local SNP members as their candidate for the Skye, Lochaber and Badenoch constituency held by Dave Thompson who would not be standing at the next election. She was part of an SNP campaign to address the gender pay gap around employment in the Highlands. She was elected in the 2016 Scottish Parliament election. Until her promotion to the Scottish Government, she chaired the Scottish Parliament's Cross-Party Group on Gaelic and has spoken in favour of UNESCO Intangible Cultural Heritage status as a possible way to protect the language. In March 2018, she delivered an entire speech to the Parliament in Gaelic during a plenary debate on the language. A member of the Free Church of Scotland, Forbes called on the Governmentto let children practice religious belief in school without mockery. In May 2018, she said "I wanted to note that pupils should be allowed to explore, develop and understand the diversity of religious faith in Scotland because if they can understand it in school you will hope that as they go through the rest of their life they will be tolerant of people who believe that things are different to them." On 27 June 2018, she was appointed to the Scottish Government as Minister for Public Finance and Digital Economy, as part of a wider reshuffle announced by First Minister, Nicola Sturgeon. On 6 February 2020, she became the first woman to deliver the Scottish Budget upon Derek Mackay's resignation as Cabinet Secretary for Finance, Economy and Fair Work. Prior to this, no woman had delivered a Budget in either the Scottish Parliament or Westminster, although they have in the Welsh and Northern Ireland Assemblies. On 17 February, she was appointed Cabinet Secretary for Finance—the first woman to hold the post.