In spite of belonging to a previous generation, he considered himself fully integrated into Modernisme. A. Mestres was an important figure for the movement, as he was the reference point for the Modernista illustrators and was the driving force behind a new school.

In the 1870s he contributed actively as an illustrator to publications such as La Campana de Gràcia and L'Esquella de la Torratxa, and as a writer to newspapers such as La Publicitat. He conceived books as a total art form and so his work embraced everything from writing (both prose and poetry) to illustrations, which he regarded as a form of expression on a par with the text and not as a complement to it or a support for it. These features can be seen in one of his most successful works, Liliana (1907), which is often regarded as an example of his Modernista production. Some of his poems were set to music by E. Granados and E. Morera.

His career, during which he produced a large number of drawings, was cut short by blindness around 1920.

Most of his lyrical and dramatic work was set to music by E. Granados, A. Vives and E. Morera.