In 1883-1884, Enrico Catellani undertook teaching international law, diplomacy and the history of treaties at the University of Padova. In 1888, he won a competition to be a full professor at the Royal University of Pisa, but he rejected the assignment in order to remain close to his home city: he became a full professor at the University of Padova beginning in the 1890-1891 academic year where he served for almost 50 years.

Photo of the façade of Palazzo Bo, before the opening of the portico, inaugurated in 1942.
Courtesy of the University of Padova, Servizio gestione documentale.
Settore Archivio di Ateneo, raccolta fotografica, foto 0012

Photo of Palazzo Bo, on the Via Cesare Battisti side, prior to renovations in the mid-thirties.
Courtesy of the University of Padova, Servizio gestione documentale.
Settore Archivio di Ateneo, raccolta fotografica, foto 0363

Bettanini wrote that “un affetto paterno lo avvinceva agli scolari. A quelli che sceglievano dissertazioni di laurea nelle discipline da lui professate, era prodigo di consiglio e assistenza …” : “a paternal affection endeared him to students. He was generous with advice and assistance to those who chose to study for a degree in his subject area…” (Commemoration, p. 10).
An example of his thoughtful and open approach to teaching can also be seen in a letter from 12 November 1900 addressed to Angelo Sullam (1881-1971), who later became a prominent exponent of Italian Zionism. He was a young man about to take his first steps in the drafting of his thesis and in need of steady guidance to properly undertake his research: Catellani suggested to him the best suited texts and journals about Judaism and, in particular, the 1878 Treaty of Berlin. He also urged Sullam to learn English, if he did not already know it, since he believed that the subject of his thesis was covered more thoroughly in works written in that language. The professor closed his letter declaring himself, “always available for further research.” Sullam then graduated in 1902, with Catellani as his advisor, with a thesis entitled: “Il sionismo specialmente considerato nei suoi rapporti col diritto internazionale” (Zionism and, In Particular, Its Relationships with International Law) (Centro documentazione ebraica contemporanea, fondo Sullam, busta 1, fasc. 8).

He also had positions in other cities: from 1904 to 1915, he taught the history of colonies and colonial law and history of treaties at the università Commerciale Bocconi in Milan, and from 1919 to 1931 he was Professor of International Law at the Regia Scuola Superiore di Commercio di Venezia.

Group photo. 1930-1931 academic year undergraduates of the Reale Scuola Superiore di Commercio di Venezia, with teachers.
From the Bollettino della associazione “Primo Lanzoni” fra gli antichi studenti
della R. scuola superiore di commercio di Venezia, XXII, 1931, n. 100 , aprile-settembre
(Ca' Foscari Fondo Storico - BG P U 541/1 - © Università Cà Foscari Venezia)

He was appointed Senator of the Kingdom on 3 october 1920.

In a letter dated 6 May 1931, the rector Giannino Ferrari Dalle Spade informed Catellani of his retirement due to age, effective 1 November of the same year. The jurist responded with a letter on 8 May 1931 in which he expressed his sorrow at the news, although awaited, and at the same time, the comfort he felt by the words of appreciation and gratitude expressed by the rector, not only in his official capacity in the name of the Ministry and the academic staff, but also in his personal capacity as a former student.
Catellani deeply loved his profession which he considered as a mission: “I so identified with the mission of teaching that I would have continued with enthusiasm, even in the economic conditions of a pensioner, had the law allowed it”  (University of Padova - Ufficio gestione documentale, Professori di ruolo incaricati e cessati, fascicolo Catellani Enrico, lettera 8 maggio 1931).  He was nevertheless allowed to remain at the University as “a professor in a private capacity”.
In the same year, 1931, he received an degree ad honorem from the University of Cambridge, while in 1932, the Ministry of National Education rejected his nomination as Professor Emeritus, proposed by the Faculty of Law of the University of Padova.

As an expert in aviation law he was called to participate in commissions for assigning aeronautical patents.

He was active in many institutions in his own city:

• Accademia Patavina di Scienze, Lettere ed Arti (now Accademia Galileiana di Scienze Lettere ed Arti in Padova), he was president from 1926 to 1928
• Member of the Commissione Permanente della Regia Biblioteca Universitaria

• Istituto Veneto di Scienze, Lettere ed Arti di Venezia dal 1885, he was president from 21 December 1919 to 21 December 1921.
• American Institute of International Law
• International Law Association
• International Colonial Institute
• Institut de Droit International
• Istituto Coloniale Italiano
• League of Nations
• Institut für Internationale Recht di Kiel
• Ministero degli Esteri for which he was a consultant and diplomat
• Ministero di Grazia e Giustizia for which he was a consultant

A photographic record of his participation in the Institut de Droit International at the sessions of Paris (1934) and Brussels (1936) is available:

His scientific output and the spirit in which he was present in academic life were recalled by Anton Maria Bettanini, in the Commemoration held on 16 May 1947 at the University of Padova.