Lasko grew up in Berlin, where his father worked in the film industry. The family moved to England in 1937. He attended Saint Martin's School of Art, but soon switched to art history, studying at the Courtauld Institute from 1946. In 1950 he became assistant keeper in the Department of British and Medieval Antiquities at the British Museum, where he remained for 15 years.
In 1965, he became the first professor of art history at the University of East Anglia. After eight years in the position left to become Director of the Courtauld Institute, succeeding Anthony Blunt.
In 1972 his book Ars Sacra, dealing with works made for church treasuries between 800 and 1200, was published as part of the Pelican History of Art. 
Following his retirement from the Courtauld he devoted much of his time to the "Corpus Of Romanesque Sculpture In Great Britain And Northern Ireland", a project he took over from George Zarnecki, and a book on German expressionist art, which was published after his death.
- The Kingdom of the Franks: North-west Europe Before Charlemagne. (1971)
- Ars Sacra: 800-1200 (1972)
- Medieval Art in East Anglia, 1300-1520 (1973).
- The Painting Collections of the Courtauld Institute of Art (1979).
- The Expressionist Roots of Modernism (2003).
- "Peter Lasko". The Guardian. 29 May 2003. Archived from the original on 26 April 2013. Retrieved 26 April 2013.
- Sorensen, Lee (ed.). "Lasko, Peter [Erik]". Dictionary of Art Historians. Archived from the original on 26 April 2013. Retrieved 26 April 2013.
- "A History of the Courtauld". The Courtauld Institute of Art. Archived from the original on 26 April 2013. Retrieved 26 April 2013.
- Heslop, T.A. (28 May 2003). "Peter Erik Lasko Obituary". The Independent.