The foundation that awards the prize said his designs convey both "power and modesty, bravado and subtlety".
The honor, often dubbed the Nobel prize for architecture, was supposed to be announced next month and presented in Washington, DC, but was prematurely reported by a news outlet, according to a spokesman.
The annual prize, which goes to a living architect, is endowed by the wealthy Chicago-based Pritzker family, majority owners of Hyatt Hotels Corp and other businesses.
It was first bestowed on American architect Philip Johnson in 1979, and has since been awarded to architects from around the world including Souto de Moura's former teacher Alvaro Siza in 1992.
"The fact that this is the second time a Portuguese architect has been chosen makes it even more important," Souto de Moura, 58, said in a statement issued by the foundation.
Among the Souto de Moura's Portuguese projects are a soaring stadium in Braga, the Burgo Tower in Porto, a convent restored as an inn in Amares, a subway in Porto, the Paula Rego Museum in Cascais, as well as shopping centers, schools, art galleries, homes and a cinema.
Most of the Porto-based architect's designs are in Portugal, but some have been built in Spain, Italy, Germany, the United Kingdom, and Switzerland.
"During the past three decades, Eduardo Souto de Moura has produced a body of work that is of our time but also carries echoes of architectural traditions," Lord Peter Palumbo, the prize jury chairman, said in the statement.
"His buildings have a unique ability to convey seemingly conflicting characteristics -- power and modesty, bravado and subtlety, bold public authority and a sense of intimacy -- at the same time," he said.
Among influences cited for his work are the sleek, spare designs of Mies van der Rohe, with his angular constructions employing granite, wood, marble, brick, steel, concrete -- sometimes in unexpected colors.
The granite face of a mountainside -- created with precise explosions with the detritus crushed for concrete -- forms one end of the stadium in Braga, which the Pritzker jury commended as "muscular, monumental and very much at home within its powerful landscape."
-Reuters
