MacIntosh joined the Foreign and Commonwealth Office (FCO) in 1991 and served at the UK missions to the UN in New York and Vienna, and in the British embassy in Madrid. She was strategy coordinator for the UN mission in Kosovo 2004–05, and High Commissioner to Sierra Leone (and non-resident ambassador to Liberia) 2006–08. She then took a fellowship at the Weatherhead Center for International Affairs at Harvard University 2008–09. She was Director, Strategic Finance at the FCO 2009–11, Director, Defence and International Security 2011–14, and Director General, Defence and Intelligence 2014–16. In November 2016 the FCO announced that she had been appointed Permanent Representative to the United Kingdom’s Delegation to NATO. She took up the post in February 2017.
Already Companion of the Order of St Michael and St George (CMG), she was appointed Dame Commander of the Order of St Michael and St George (DCMG) in the 2020 Birthday Honours for services to British foreign policy.
- MacINTOSH, Sarah, Who's Who 2016, A & C Black, 2016 (online edition, Oxford University Press, 2015, accessed 23 Nov 2016)
- "Change of UK Permanent Representative to NATO". Foreign & Commonwealth Office. 4 November 2016. Retrieved 23 November 2016. CS1 maint: discouraged parameter (link)
- "Sarah MacIntosh CMG, UK Permanent Representative to the North Atlantic Council". gov.uk. Retrieved 10 February 2017. CS1 maint: discouraged parameter (link)
- "No. 63135". The London Gazette (Supplement). 10 October 2020. p. B3.
- "Order of St Michael and St George awards in the Birthday Honours Diplomatic Service and Overseas List 2020 - GOV.UK". assets.publishing.service.gov.uk. Retrieved 9 October 2020.
| High Commissioner to Sierra Leone
| Ambassador to Liberia (non-resident)|
Sir Adam Thomson
| Permanent Representative to NATO