Retracing the architectural sequence of events of the Church of Saint Sebastian from its beginnings means immersing oneself in the Middle Ages, when the small Church of Saint John was erected on this site. The fading away of the Confraternity of the same name at the end of the fifteenth century brought about the first renovation of the building, which maintained the old name, yet added the worship of Saint Sebastian. 

No trace of the sixteenth-century church has survived yet there is much information which refers to it. We know that not only was the interior frescoed with the stories of the Martyrdom of Saint Sebastian, but that the façade also had a painting with the two saints James and Sebastian on the sides of the Crucifix. The building survived until the second half of the XVI century, when the wartime events necessitated its reconstruction, begun at the end of the same century. The first works concluded with the façade in 1621 and the new church was consecrated four years later. Throughout the entire course of the XVII century, the Confraternity lavished in continuous works to enlarge and embellish the building, from Molineri’s decorations in the 1620s to the enlargement of the oratorio in 1663, enlarging the main body of the church and bringing the façade to its current position. In the subsequent century, massive works were done, including the construction of the sacristy and the Council Room as well as the renovation of the presbytery and the choir stalls (1736-54). In the XIX century, total refurbishment of the nave was required, with the opening of the two lateral chapels, the completion of the neoclassical façade (1889) and the neo-Gothic belfry (1899). The building deteriorated little by little after the Second World War, almost reaching a state of abandon. The radical restauration work that began in 2003 returned the church to its ancient splendor.

The state of disrepair of the Church of Saint Sebastian the end of the sixteenth century was the reason the ceiling of the nave was re-plastered in 1702, however twenty years would pass before proceeding with a new series of work, performed mostly to remold the choir area. In 1729, the Board proposed to intervene for a “better embellishment of this Confraternity, [...] with the use of other works in the church so as to render it decorous”, so with the deliberation on 6 May 1730, authorization is given to begin the work for the “modernization of the choir”. The work prompted the modification of the previous space, completed by master craftsmen Fontana and Scala at the end of the sixteenth century. More work was completed between 1730 and 1731, including closing off the large door which opened behind the altar (today a trace of the frame on the outer façade of the wall remains), to the completion of the two side niches and, at the same time, the construction of the new rooms adjacent to the sacristy and the Council Room. The works for the new altar are delayed until the second half of the 1730s, when in 1736 the consultation of the Monregalese architect Francesco Gallo is requested. Still in 1741 the Confraternity decided to incur the expenses for the “the restoration of the pews to be placed in the abovementioned choir”, in addition to cleaning the ancon, refurbishing the balustrade and “painting the side arches to make them uniform with the front arch and to the choir”. The current choir was made more luminous thanks to opening the windows in the niches, is therefore mostly the fruit of the eighteenth century interventions. The elegant and imposing Roman-style altar (innovative with respect to the back wall of the presbytery) was completed by replacing the wooden floor with multicolored marble, with groups of angels and cherubs in the stucco decorations by the Luganese artist Cipriano Beltramelli, also in the frontal, whose central frame has an arrow, the symbol of Saint Sebastian. The wooden choir stalls covering the back wall, following the curved movement, are separated by the presbytery area by several elements that survived from the old wooden balustrade; the area in front of the altar includes the two arms of the marble balustrade, joined by a wrought-iron gate. The decoration on the walls and on the ceiling, clearly pronounced by the frescoes in the nave completed by Toselli in the first half of the nineteenth century, is characterized by the trompe-l'oeil architecture by Pietro Antonio Pozzi, in which the fresco Glory of Paradise painted by Alessandro Trono in added on the ceiling. The central ancon with the crucifix and the saints James, Sebastian and the two confraternity brothers by Molineri, were completed during the first decades of the XVII century, which dominates the wall at the center of the presbytery, enhanced by a column and a pilaster which frame it, accentuating the monumental nature of the wall; this is an effect which we find in the evangelists painted by the same artist in the side rib vaults.