His professional career was extremely short, as he committed suicide while very young. He chiefly made sketches and pastel drawings choosing "dark", in other words, marginal subjects.

He was one of the artists who regularly attended the discussions and shows at Els Quatre Gats (Montsió, 3 bis), where he also staged an exhibition in 1900. He was extremely good friends with Picasso, with whom he shared a studio in Barcelona and went to Paris in 1900. Picasso was very upset by his death, and this is thought to be one of the factors that influenced the painter in his blue period. Some of his paintings of that time, such as La vida (Life, 1903; Cleveland Museum of Art) are dedicated to Casagemas.

He occasionally wrote articles and short stories that were published in the magazine Joventut.