Philippidis had been studying history of religions at the University of Leipzig since 1926 and had obtained his doctorate there under the supervision of Hans Haas in 1929. His stay in Germany coincided with a critical period in which National Socialism was gaining strong footholds within German society, including academia, even before coming to power in 1933.  

From 1930 until 1939 Philippidis held various political and ecclesiastical posts, including a leading one in the Ministry of Education and Religious Affairs. The institutionalization of the history of religions within the Divinity School of the University of Athens, an Orthodox denominational school, owes much to him. 

 Upon his return to Greece, Philippidis continued his research and writing activities. He taught as a Privatdozent at the Divinity School of the University of Athens from 1934 until 1939 and subsequenly as a professor of the history of religions until his retirement in 1968. Generally, Philippidis’ important contribution to this field is that he supported and developed a historical- philological approach to religions.  

Aside from his successful academic career, Philippidis obtained early enough important posts outside academia. Before going to Germany he had served as director of the Metropolitan Office for the Metropolitan of Smyrna Chrysostomos (1919-1921) and later as director of the Patriarchal Office for the Patriarch of Alexandria Photios (1923-1925). In addition, from July 1930 up to December 1939 he served as the Director of the Department of Ecclesiastical/Religious Affairs at the Ministry of Education and Religious Affairs.

Biographical information on Philippidis are taken from Makridis, V., "Leonidas Philippidis and the Beginnings of the History of Religions as an Academic Discipline in Greece“in: Horst Junginger (ed.), The Study of Religion under the Impact of Fascism (Numen Book Series. Studies in the History of Religions, 117), Leiden/Boston: Brill, 2008, 283-302