McNair was educated at St Benedict's School, Ealing and at the University of Bristol, where he was Vice-President of the University Debating Union. He has practised City oriented litigation at Lovells (now Hogan Lovells), at Lawrence Graham LLP, and, since 2012, at Cubism Law, specialising in major commercial and corporate litigation and public law cases, domestically and internationally.
In 2011 McNair acted for the successful third party interveners in A, B & C –v- Republic of Ireland, before the Grand Chamber of the European Court of Human Rights (ECHR). This was a landmark case in which the court dismissed a wide range of complaints by A, B and C, claiming lack of access to abortion facilities in Ireland. The court upheld only one complaint brought by the Claimants as to breach by Ireland of Article 8 ECHR (Right to Privacy), finding that Ireland had violated the Convention by failing to provide clear information on whether a woman was entitled to an abortion under prevailing Irish law. In light of the ABC case, the Irish Government introduced the Protection of Life During Pregnancy Bill to detail the circumstances under which abortions in Ireland could be legally performed. This passed into law in July 2013.
In 2012 he acted for successful interveners in BPAS –v- Secretary of State for Health, in the Administrative Court in London.
He was named respectively both "Lawyer in the News" (Law Society Gazette) and "Lawyer of the Week" (The Times) for his conduct of these cases.
In 2013 McNair was appointed by the RSPCA to chair a national review of its Freedom Food scheme. Serving on his panel were former cabinet minister and Secretary of State at DEFRA, the Rt Hon Caroline Spelman (MP), and Prof. David Main (BVetMed, PhD, MRCVS), Reader in Animal Welfare and Behaviour at the University of Bristol Veterinary School. Evidence was taken from all areas of animal food production, distribution and retail and from interested parties. The McNair Report was presented in May 2013. Its recommendations were unanimously approved by the Council of Trustees of the RSPCA the following month. The RSPCA later announced it is formulating a strategy to build on the recommendations of the McNair Report which formed the basis of their RSPCA Assured scheme. The scheme is dedicated to the better welfare of hundreds of millions of farmed animals across the UK and influential upon schemes affecting many billion farmed animals across the world.
McNair undertakes extensive pro bono charity work, especially in the field of animal welfare. In 2015 he founded Save The Asian Elephants, a coalition of politicians, academics, lawyers, field experts and campaigners working to protect the Asian elephant from abuse and extinction (www.stae.org).
McNair speaks and publishes widely on issues relating to animal welfare including in relation to food production, distribution and retail and problems associated with livestock supply chains.
McNair is described in his legal profession work as "indefatigable" and is named as "the client's champion" in the 2015 edition of Legal 500, a leading client and peer review of recommended UK lawyers. He is ranked by Oratto (www.oratto.co.uk), a leading UK referrer of legal work, as "excellent" in all his practice areas.
Duncan McNair was appointed a Knight of the Holy Sepulchre (KHS) by the Roman Catholic Church in 2002.
McNair has written two books, The Morello Letters – Pen pal to the stars and More Morello Letters – Pen pal to the superstars under the pseudonym of a fictional Italian immigrant, "Mrs Morello, a lover of all things British", who struggles to understand some of the more idiosyncratic aspects of British life. Both books have been widely reviewed and acclaimed. In 2012 The Morello Letters was included by BBC Radio 4 listeners amongst their funniest books ever in Open Book’s Listeners’ Funniest Books hosted by Mariella Frostrup.