Geyl was educated at the University of Leyden. Pieter was the greatest Dutch historian of his time, and a scholar of European renown. In 1913 he came to London as the correspondent for a Dutch newspaper, and in 1919 he was appointed Professor of Dutch Studies at London University. He later returned to the Netherlands as Professor of Modern History at the University of Utrecht, where he remained until his retirement in 1958. During the Second World War, he was imprisoned in a German concentration camp. He died in 1966.