Buchan is a qualified solicitor. He started his career working in corporate finance before moving in-house with the FI Group, the business founded by Dame Stephanie Shirley. He then spent 15 years as a partner in a private equity firm with responsibility for legal and compliance and latterly fundraising. Since retiring in 2015, he has been working part time as in house counsel and is a member of his children's school's fundraising and overseas development committees and the United Nations Association Finance Committee. He joined the board of Prior's Court in March 2017.