At the centre of the friary complex stands the Church of the Annunciation - a three-aisled basilica with an elongated chancel terminating in an apse. It was probably designed by Antonio Pellacini, a Lublin architect of Italian extraction. The design combines the Mannerist layout of the collegiate church in Zamość with Baroque components modelled on Jesuite basilicas. By the first half of the 17th century the church in Leżajsk was one of the main Marian shrines in the Ruthenian Voivodeship, and in the 18th century it became well-known as a place where indulgences were granted. The building was raised on the site where, tradition has it, Our Lady and St Joseph were seen in an apparition in 1590. The painting of Our Lady of Leżajsk, recognised as miraculous in 1634 (and subsequently crowned in 1752), was placed in a chapel which began to attract pilgrims. The Baroque interior dazzles the visitor with its opulence. The polychrome paintings on the church’s walls and ceilings reveal Italian influences, drawn in particular from the work of Andrea Pozzo and the quadratura painting of the Bologna school, transposed to Leżajsk through the efforts of the dynamic artistic community of Lvov. The frescoes (1750-1758) were painted by artists from Lvov: Wojtanowski and Kłosowski (first names unknown), Stanisław Stroiński, and Mateusz and Maciej Miller. Noteworthy features include the huge altarpiece (1637) in the shape of a triumphal arch above the main altar, the stalls (1649), the 17th-century pulpit and a group of side altars (c. 1752-1757), produced by the Lvov woodcarver Alojzy Osiński, who also made the tabernacle adorning the main altar. The finest work of art in the basilica is the organ, which has 74 stops and 5894 pipes. S. Studziński and J. Głowiński worked consecutively on its construction (1680-1689). The organ case and choir loft (both in the nave and aisles) are notable for their homogenous structure and decoration. The lavish ornamentation is complemented by iconographically rich figural carvings, including a famous representation of Hercules fighting the Hydra. The monastery is home to the Museum of the Observant Franciscan Province in Poland, featuring valuable collections of ecclesiastical art and a unique collection of books from monasteries of Poland’s pre-war eastern (Kresy) territories.

The importance of the monastic complex at Leżajsk stems not only from the artistic merit of its buildings and their contents, which are undoubtedly among the finest ecclesiastical historic monuments in Poland. Over the centuries, and to this day, the monastery has played an important cultural role. The Franciscans and their patronage of the arts, through which they hoped to enhance the renown of this holy site, distinguished by the miraculous image of Our Lady, helped to create architecture, paintings and carvings which were significant on more than just a local scale. They managed to commission the greatest artists, whose work inspired artistic development in smaller regional centres. They also managed to unite wealthy benefactors, such as the Opaliński, Grabiński and Potocki families, to help achieve their objectives.