The architecture of the church is in neo-Renaissance style with a wide apse and a single nave housing columns, pilasters and capitals. The high altar is located at the centre of the apse, whereas the two lateral altars are in the nave.
The organ, placed above the entrance with a decorated chancel (18th century) was built in 1793 by the famous Gaetano Callido from Venice for the church of St. Francis in Fabriano, no longer extant, and it was moved to Sigillo in 1869. It is still today the first and only original of this maker existing in Umbria.
The walnut choir with wide stalls and an imposing lectern, dated 1679, is also very interesting. Above the choir is an 18th-century painting with a rich frame, depicting the Martyrdom of St. Andrew.