He wrote many books about the Orthodox Church, and about Christianity in Russia, of which the best known is The Russian Religious Renaissance of the Twentieth Century (1963).
He himself began medical studies in Moscow in 1917, but after the Russian revolution and civil war his family fled to the Caucasus, arriving in Georgia in 1920.
Nicolas was a founder of the Brotherhood of St Seraphim of Sarov, and in Paris from 1926 to 1929 was secretary of the Russian Student Christian Movement, and first editor of their periodical, Vestnik Russkogo studencheskogo Dvizheniya" In 1927 he married Militza Vladimirovna Lavrova (Милице Лавровой, 1899-1994), who was a doctor and a dental surgeon, practising in a London hospital.
In 1947 Zernov gave up his secretaryship of the Fellowship and began teaching in Oxford University, as Spalding Lecturer in Eastern Orthodox Studies.
For two short periods he left Oxford, to serve as Principal of the Catholicate College Pathanamthitta in Kerala, India (1953-1954) and as Visiting Professor of Ecumenical Theology, Drew University, New Jersey, USA (1956).