Dr Macmillan specialises in assisting individuals and businesses authenticate, certify and Apostillise critical documents for use internationally. His law firm, Peter Macmillan & Associates, is one of the most in-demand boutique Notary Public practices in Australia.

Dr Macmillan is also the Founder of The Macmillan School of Practising Lawyers, provides pro bono attestation services to local businesses and individuals, and, as a cognitive scientist, writes books and teaches on the development of legal expertise.

A lawyer for over 30 years, Dr Macmillan has held various positions in governments and law firms in Australia and internationally, including as a senior investigator with the Australian Competition and Consumer Commission, a legal specialist with two top-tier Australian law firms (Allens and Clayton Utz), a government policy representative in Geneva (while with the Hong Kong Office of the Telecommunications Authority), and as Head of Competition Law at Hong Kong's largest law firm (Johnson Stokes & Master, now Mayer Brown).

After completing his PhD in cognitive science and law in 2015 (at the University of Queensland and Bond University), he founded Meisterline® Analytics, a London-based research lab that went on to develop the world's first quantitative method for measuring legal expertise using the KUJI® Rating Scale.

Dr Macmillan holds Bachelor’s degrees in Economics and Law from the University of Tasmania and a Master of Laws degree from Melbourne University.

He is the author of several books on the development of professional expertise, including Unlocking the Secrets of Legal Genius: Measuring Specialist Legal Expertise Through Think-Aloud Verbal Protocol Analysis (2015), The KUJI® Handbook (2020) and The 21 Secrets of Gritty Professionals (2022). He is also Series Editor of The Legal Intern Diaries: Becoming a Lawyer with Dr Peter Macmillan (2024).