On 20 March 1402, master mason Giovanni Borri began to rebuild a place of worship over the foundations of the medieval church. What is now the cathedral emerged in about 1000 and rebuilding began in 1402.
The medieval church was probably built before the foundation of the commune and stood on the area where it can still be seen, but was smaller in size. Several surviving stone capitals were used to decorate the semi-columns of the choir and of the final aisle arches in the 1402 reconstruction.
Rebuilding was concluded after 1404 but work continued for over a century to finish the trim and decorations.
The oldest and most and important testimony to the reconstruction of the church is found on a green stone plaque, now walled next to the left door in the façade, commemorating the day work was started under master mason Giovanni Borri. The church was enlarged in the 18th and 19th centuries by royal decree to make it more suited to its new role as a cathedral, following Biella’s elevation to diocese.
No traces remain of the ancient chapels following the extensions added to elevate the church to rank of cathedral. The task of overseeing the work of extension and refurbishment ordered by King Charles Emmanuel III was entrusted to Turin architect and hydraulic engineer, Ignazio Giulio. On 10 April 1772 this architect drew up a detailed report that provided both a description of the ancient church, including details not known until that moment, and also a meticulous description of the stages of the project.
The project proposals implemented included the opening of oval windows along the church; the repair of the foundations of both naves; the great sacristy; the chapterhouse; the extension of the transepts for the Epiphany and Holy Sacrament chapels.
On 16 June 1804, during Napoleonic rule, Monsignor Canaveri consecrated the church. The events leading to the fall of the Kingdom of Piedmont and start of the Napoleonic regime contributed to damping the fervour for the expansion and embellishment of the cathedral.
In about 1817, after the death of architect Ignazio Giulio, the position of superintendent for the cathedral site was entrusted to another architect, Nicola Martiniano Tarino .
The tasks that required most work were the lengthening of the church’s nave and two aisles, together with the construction of a new façade and a large porch. The Biella architect Felice Marandono was appointed to draw up the designs.
Marandono suggested an eclectic architecture using Neogothic language enriched with Egyptian-style Neoclassical elements.
The final phase of renovation began in 1926, with the restoration of cathedral and belfry. The 18th and 19th-century interventions, and subsequent 20th-century restorations contributed to Biella cathedral’s complex, layered identity.