He studied at the Barcelona School of Architecture, with teachers such as L. Domènech i Montaner and others who had already begun to use artistic styles that pointed the way to Modernisme, and qualified as an architect in 1891. Thanks to his professional career as an architect, but also as a historian, he has become one of the most representative figures of Modernisme.

While still a young man he already began to stand out for his knowledge of Romanesque architecture with the publication of articles in the magazine La Renaixença on Catalan archaeology and architecture, the subjects of the book L'arquitectura romànica de Catalunya (The Romanesque Architecture of Catalonia, 1909-1916), which he was later to write in collaboration with A. Falguera and Josep Goday.

In 1892 he obtained the post of municipal architect of Mataró, a town where he did some public sector works, but he started to receive commissions from private individuals, such as the one to build Casa Garí (1898; Camí de Sant Miquel del Cros, 9, Argentona).

The first building he constructed in Barcelona was Casa Martí (1895-1896; Montsió, 3 bis), in Neo-Gothic style, the ground floor of which was occupied by the Quatre Gats café. In 1896 A. Gallissà took charge of directing the works and this became the first venture on which the two architects worked together. This first commission was followed by many others, such as Casa Amatller (1898-1900; Passeig de Gràcia, 41), Casa Macaya (1899-1901; Passeig de Sant Joan, 108), the former Casaramona factory (1910-1913; Marquès de Comillas, 6-8; which since 1998 has housed the CaixaForum space) and Casa Pich i Pon (1921; Plaça de Catalunya, 9), regarded as Noucentista ("1900-ist", a term coined in 1906 to refer to 20th century Catalan culture), to name but a few. In all of them there is a clear influence of North European Neo-Gothic architecture to which elements of the long tradition of popular Catalan architecture have been applied.

Apart from constructing buildings, he helped to design the decoration of various establishments such as the Torino café (1902; Passeig de Gràcia, 18; no longer in existence), together with A. Gaudí and P. Falqués, and the Sastre i Marquès chemist's shop (1905; Hospital, 109; no longer in existence). Works by him are also to be found in other parts of Catalonia, such as Lloret de Mar, Terrassa and Sant Sadurní d'Anoia, and other cities in the rest of Spain.

His desire to modernise the country led him very early on to become involved in Catalan politics, first as a city councillor in Barcelona, then as a deputy to the Spanish Parliament in Madrid and finally as president of the Mancomunitat de Catalunya, a body bringing together Catalonia's four provincial councils (1917). In 1942 he was appointed chairperson of the Institute of Catalan Studies.