Zeeman studied physics at the University of Leiden under Kamerlingh Onnes and Hendrik Lorentz. In 1890, even before finishing his thesis, he became Lorentz's assistant. This allowed him to take part in research on the Kerr effect. In 1893 he submitted his doctoral thesis on the Kerr effect, the reflection of polarized light on a magnetized surface. He then went for six months to Friedrich Kohlrausch's institute in Strasbourg. In 1895, Zeeman came back from Strasbourg to teach mathematics and physics in Leiden. He married Johanna Elisabeth Lebret (1873–1962); they had three daughters and one son.