Passionate about the world of drawing, Casas left his studies when he was 11 to dedicate fulltime to his artistic vocation. He was only 15 years old when he went to Paris, where he took classes with Carolus-Duran.
In 1882, he exhibited for the first time in Barcelona, but he soon returned to Paris, where he lived a comfortable bohemian life, initiating his long friendship with Rusiņol and Utrillo, and meeting other artists such as Puvis de Chanvannes and Zuloaga. This environment led him to paint with contained color, toned-down lines and subject matters from interiors as well as outdoors.
Once again settled in Barcelona in 1897, Casas and the painters Utrillo and Rusiņol opened the bar Els Quatre Gats, where they took the lead in activities of the most avant-garde nature and led round tables dealing with subjects related to art nouveau. This enabled them to meet the artists of the young generations such as Picasso, Nonell, Mir and the musicians Albeniz and Granados. Over the following years, prolific and in great demand, Casas illustrated magazines (Pel & Ploma, Quatre Gats), produced advertising posters (Anis de Mono, Paris Cigarettes), and painted many portraits.