The site of the Cathedral was originally occupied by a three-nave Romanic church whose earliest mention dates back to 1262. After the fire of 1361 it was re-vaulted in the Gothic style. When the Ljubljana Diocese was established in 1461, the church underwent several alterations and additions. In 1469 it was burnt down, presumably by the Turks.
Between 1701 and 1706, a new Baroque hall church with side chapels shaped in the form of the Latin cross was built to a design by the Jesuit architect Andrea Pozzo. As the church's dome was only built in 1841, originally a fake dome was painted on the arch above the centre of the cross. The surviving Baroque interior decoration notably includes frescoes by Giulio Quaglio (painted in the periods 1703-1706 and 1721-1723), Angelo Putti's statues of four bishops of Emona situated beneath the beams of the dome (1712-1713), Putti's painting of Dean Janez Anton Dolničar (1715), who initiated the rebuilding of the church in 1701, Francesco Robba's altar angels in the left part of the nave (1745-1750) and brothers Paolo and Giuseppe Groppelli's altar angels in the right part of the nave (1711).
A host of other works of art were added later. One of the more interesting is the dome fresco painted by Matevž Langus in 1844. The most outstanding 20th century additions include Tone Demšar's main entrance door relief depicting the history of Slovenia, commissioned to mark the 1250th anniversary of Christianity in Slovenia, and Mirsad Begić's side doors with portraits of bishops.