The episcopal see for the Portuguese diocese of Porto is the Porto Cathedral, or Sé do Porto. One of the largest and oldest monuments in the city, it is situated in the centre of the historic district.

Its construction lasted from the first part of the 12th century to the 13th century's beginning. Over the years, this first structure, which was constructed in the Romanesque style, experienced numerous changes. The three naves and barrel-vaulted body of the church, as well as the façade's overall design with its towers and stunning rose window, are all remnants of the Romanesque era. The Porto Cathedral was one of the first Portuguese structures to incorporate flying buttresses to support the ceiling of the central nave.

The Gothic era saw the construction of the funeral chapel for Joo Gordo, a Hospitaller Order knight and ally of Dionysius I of Portugal who died in about 1333. The cloister, which was constructed between the 14th and 15th centuries under John I of Portugal, is another Gothic-era structure. At 1387, this king wed Felipa of Lancaster in the cathedral of Oporto.

The Baroque era saw significant changes to the cathedral's exterior. The ancient Romanesque entryway was replaced by a new one sometime around 1772. The towers' domes and balustrades are both Baroque. The side façade of the church received a stunning Baroque narthex addition by the Italian architect Nicolau Nasoni in 1736. A splendid silver altar, constructed by many Portuguese craftsmen in the second half of the 17th century and located to the left of the apse, was rescued from the French forces in 1809 by a hurriedly constructed plaster wall. A Baroque high altar was installed in its place of the ancient Romanesque high altar (which had an ambulatory) in the 17th century. The main altar, which was created between 1727 and 1729, is a significant example of Joan Baroque art. It was created by Miguel Francisco da Silva and Santos Pacheco. Nasoni created the mural paintings in the main chapel.

The Chapel of San Vicente and the 14th-century cloisters are accessible via the south transept. The upper levels are accessed by a lovely Nasoni staircase from the 18th century, which leads to tiled panels that illustrate Ovid's Metamorphoses and the Virgin's Life.

The Cathedral is home to three exquisite organs. One of them, in the choir loft, commemorates a time when organ development began in Portugal. It is an organ by the same builder as the organ in the Lapa (Porto) church; both were supported by Ferreira dos Santos' efforts and initiative.