He is best known for his monumental Italia sacra, a massive nine-volume treatise detailing the history of all Italian dioceses from the earliest Christian centuries to his day.

In the 1620s Ughelli worked, together with the Luke Wadding, Andrea Vittorelli, Girolamo Aleandro, and Cesare Becilli to the revision of Ciacconius' Vitae et Res gestae Summorum Pontificum et S.R.E.

[4] To encourage him in this work and to defray the expense of the journeys it entailed, Pope Alexander VII granted him an annual pension of 500 scudi.

[5] He was a consultor of the Index Librorum Prohibitorum and theologian to Cardinal Giancarlo de' Medici; he was frequently offered the episcopal dignity, which he refused.

[3] Ughelli's work was abridged by Giulio Ambrogio Lucenti (Rome, 1704) and republished, with corrections and additions, by Nicola Coleti (10 vols, Venice, 1717-22).

Ughelli's work exerted a great influence on Gams' Series episcoporum ecclesiæ catholicæ (1873-86) and on Eubel's Hierarchia Catholica Medii Aevi (1913–1967).