Nikolai Efremovich Andreyev emigrated with his parents to Estonia in October 1919. In 1927, he graduated from the Tallinn Russian Gymnasium. He then traveled from Estonia to Germany, and from there by train to Prague, Czechoslovakia. In 1932, Andreyev completed his studies at the Faculty of Philosophy of Charles University in Prague, being a personal scholarship holder of the President of Czechoslovakia, Tomas Masaryk. In 1933, he received a Doctor of Philosophy degree, defending a dissertation on the topic "The Case of Deacon Viskovatyy as an Ideological and Literary Phenomenon."

Andreyev was a participant in the Kondakov Seminar starting in 1931, became its collaborator, and from 1933, a full member. From 1932, he worked as a librarian, from 1935 he was on the board, and from 1939 to 1945, he effectively led the N.P. Kondakov Archaeological Institute in Prague and Belgrade. He taught courses on the history of Russian literature and the history of Russia at the Russian Free University in Prague. He was a member of the literary association "Skit," the Circle for the Study of Modern Russian Literature at the Russian Free University, the Union of Russian Writers and Journalists in Czechoslovakia, the Russian Historical Society, and the Society of Friends of the Russian Hearth in Czechoslovakia. He also participated in the meetings of the National Union of the New Generation.

In the spring of 1945, with the approach of Soviet troops, Andreyev decided to stay in Prague to preserve the collections of the Kondakov Institute. On May 22, 1945, he was arrested by SMERSH, and until 1947 he was imprisoned in Czechoslovakia, and then near Dresden in Germany. In 1947-1948, he lived in Berlin. From 1948, Andreyev taught at the Department of Slavic Studies at Cambridge University in the UK, and from 1973, he became an extraordinary professor of Slavic studies. In 1955, he obtained British citizenship.

Nikolai Andreyev is buried in the cemetery of St. Andrew's Church in Girton, Cambridge, UK.