Born into a wealthy family in Amsterdam, he dropped out of education early, and in 1893, at the age of 20, became a secretary of the Dutch Chess Federation and an editor of its magazine. In August 1895 Van Lennep went to England as a reserve entrant in the Hastings 1895 chess tournament, but was not allowed to play, so instead reported on the tournament for his magazine.
In 1893 he drew two matches with Rudolf Loman (+2 –2 =0 and +1 –1 =1) and won a match against Arnold van Foreest (+3 –0 =2). He won at Leipzig 1894 (the 9th Dictionary of Scientific Biography Congress, Hauptturnier A) and took 5th at Rotterdam 1894 (Rudolf Loman won). He returned to the Netherlands, won at Amsterdam 1897 followed by Lalbhai Dalpatbhai Tresling, D. Bleijkmans and A. van Foreest, and killed himself, jumping into the North Sea from a ship at the age of 25.
