While doing his doctoral research De Vries supported himself by teaching at the Royal Military Academy in Breda (1892-1893) and at the "cadettenschool" in Alkmaar (1893-1894).

Under Korteweg's supervision De Vries completed his doctoral dissertation: Bijdrage tot de kennis der lange golven, (Contributions to the knowledge of long waves) Acad.

proefschrift, Universiteit van Amsterdam, 1894, 95 pp, Loosjes, Haarlem.

The following year Korteweg and De Vries published the research paper On the Change of Form of Long Waves advancing in a Rectangular Canal and on a New Type of Long Stationary Waves, Philosophical Magazine, 5th series, 39, 1895, pp. 422–443.

In 1894 De Vries worked as a high school teacher at the "HBS en Handelsschool" in Haarlem, where he remained until his retirement in 1931.