Although dedicated to St. Catherine, Zejtun’s first parish church is commonly known as St. Gregory’s because of the annual pilgrimage to this place. It is one of Malta’s finest old churches. Very little remains of the original rectangular church built before 1436, the time when Żejtun became a separate parish, apart from Mdina and Vittoriosa.

This present church was constructed on and around the site occupied by the old medieval church, so that the present edifice dates from the sixteenth century. For about three centuries this building served as the parish church for all the south-east of Malta. One cannot fail to admire the Gothic and Romanesque styles of architecture. The primitive dome is the most ancient example of Maltese cupolas still standing. Of particular interest is also the orientation of the south-east transept of the church which is aligned with the bays of Marsxlokk, St.Thomas and Marsakala, since the church also doubled as a watch tower. The church occupies the highest point overlooking the harbours in the South, favourite landing place for barbery corsains.

Near the St. Gregory's Church there is the statue of Pope St. Gregory the Great and the three cemeteries of Żejtun, Saint Rocco (the oldest one), St. Gregory and St. Catherine's. 

Around the dome of the Old Parish Church there is a secret passage in U-Form. Secret passages built in the thick walls of the southern transept afforded a hidden look-out for sentries who watched for the landings of the pirates in the non-distant bays and then relayed news of the pending invasion to the locals and warned the garrison of Mdina in the north by means of smoke signals from the roof of the church.

The secret passage was discovered in the 1960s where found considerable amount of human bones. The story beliefs these were buried alive with these passages during the last siege of 1614. One can still notice these bones in the secret passages.