He left Hungary in 1956, subsequently completing a DPhil at Nuffield College, University of Oxford under the supervision of C. A. Macartney and John Plamenatz.

László Péter published extensively on the constitutional history of Hungary and the Habsburg monarchy, mostly in the nineteenth century.

During the Hungarian Revolution of 1956, Péter was appointed to the revolutionary committee charged with the supervision and cataloguing of the archives of the Ministry of the Interior.

His report on his activities, compiled shortly after his flight to the UK, is published in (eds Péter and Martyn Rady) Resistance, Rebellion and Revolution in Hungary and Central Europe: Commemorating 1956, London (UCL SSEES), 2008, pp. 321–40.

Some of Péter's most significant essays and studies were collected, edited and published in Hungary's Long Nineteenth Century: Constitutional and Democratic Traditions in a European Perspective.