Gaudí was an ardent Catholic, to the point that in his later years, he abandoned secular work and devoted his life to Catholicism and his Sagrada Família. It is for this that Gaudí is known to many in Spain as "God's Architect". Soon after, his closest family and friends began to die. His works slowed to a halt, and his attitude changed. Perhaps one of his closest family members – his niece Rosa Egea – died in 1912, only to be followed by a "faithful collaborator, Francesc Berenguer Mestres" two years later. After both tragedies, Barcelona fell on hard times, economically. The construction of La Sagrada Família slowed; the construction of La Colonia Güell ceased altogether. Four years later, Eusebi Güell, his patron, died.

Perhaps it was because of this unfortunate sequence of events that Gaudí changed. He became reluctant to talk with reporters or have his picture taken and solely concentrated on his masterpiece, La Sagrada Família.

On June 8 1926, Antoni Gaudí was run over by a tram. Because of his ragged attire and empty pockets, multiple cab drivers refused to pick him up for fear that he would be unable to pay the fare. He was eventually taken to a pauper's hospital in Barcelona. Nobody recognized the injured artist until his friends found him the next day. When they tried to move him into a nicer hospital, Gaudí refused, reportedly saying "I belong here among the poor." He died two days later on June 10th, 1926, half of Barcelona mourning his death. It was, perhaps, fitting that he was buried in the midst of his unfinished masterpiece, La Sagrada Família.

Gaudí's first works were designed in the style of gothic and traditional Spanish architectural modes, but he soon developed his own distinct sculptural style. French architect Eugene Viollet-le-Duc, who promoted an evolved form of gothic architecture, proved a major influence on Gaudí. But the student surpassed the master architect and contrived highly original designs – irregular and fantastically intricate. Some of his greatest works, most notably La Sagrada Família, have an almost hallucinatory power.

He integrated the parabolic arch and hyperboloid structures, nature's organic shapes, and the fluidity of water into his architecture. While designing buildings, he observed the forces of gravity and related catenary principles.•

The architect's work has been categorized as Art Nouveau architecture, a precursor to modern architecture. But his adoption of biomorphic shapes rather than orthogonal lines put him in a category unto himself (in Latin, sui generis). His style was later echoed by that of Austrian architect Friedensreich Hundertwasser (1928–2000).

Though hailed as a genius, some hypothesize that Gaudí was color blind and that it was only in collaboration with Josep Maria Jujol – an architect twenty seven years his junior whom he acknowledged as a genius in his own right – that he produced his greatest works.