In total Lermusiaux competed in four different events at the 1896 Summer Olympics, he won his preliminary heat of the 800 metres with a time of 2:16.6, he withdrew from the final which was to take place three days later but decided to save himself for the marathon which was taking place a day after the 800 metres final. In the 1500 metres event, which was conducted in a single race, Lermusiaux led from the start, but in the final straight was passed by Edwin Flack and Arthur Blake, and finished third.