After graduating with honor in modern history, in November 1984, under the supervision of Prof. Rosario Villari, with a thesis on the persecution of witches in Italy, from 1985 Paolo Portone begins collaborating with Prof. Attilio Agnoletto, full professor of History of Christianity at the Università Statale of Milan, on a research project, afferent to the budget quota established by the CNR (National Research Council), on the history of Lombardy between the XV and the XVIII century, the results of which are published in the journal “Studies and Sources of Lombardy’s History - Books of Milan”. For the studies conducted in libraries and in Roman archives on Catholic demonology and on the elaboration of the notion of "diabolical witch" he is invited, in 1983, to attend the conference ”Hermetic Rome: exoteric culture and society in Rome between the XV and the XVIII century”, organized by the department of Paleography, presided over by Prof. A. Petrucci, with a presentation entitled “The trials against witches in Italian religious history (XV-XVIII century): research notes on the primary sources of the phenomenon of persecution.

In 1987 he begins studying sources to reconstruct the history of the Dominican Order in the ancient diocese of Como in the General Archive of the Order of Preachers, in Santa Sabina. During the same year, he attends the conference “Como and Aquileia”, organized by the Historical Society of Como, with a presentation on the convent of St. Giovanni Pedemonte (the base of the Inquisition in Como). In 1988 he is invited to the convention “Art and history in the S. Tommaso of Pavia”, sponsored by the University of Pavia, for research conducted on certain unpublished documents from the Secret Archive of the Vatican pertaining to the dismissed Dominican convent.

In October 1988 he takes part in the first national conference on witchcraft “Triora 1588: Witch hunt”, organized by the University of Genoa. In 1991, in Offagna (province of Ancona), he participates in the conference “Winged enigmas”, organized by Prof Franco Cardini, with a presentation on intermediary demons between earth and sky. In 1992, in Florence, he takes part in the first national conference called “The dimensions of consciousness”, sponsored by the Regional Administration of Tuscany and by the Municipality of Florence, with a presentation on witches’ ointment and on the late 1500s debate on the reality of magical powers.

In 1994 he recovers, in the diocesan Archive of Milan, a letter sent in 1569 by the Congregation of the Holy Office to [Cardinal] Carlo Borromeo, with which the Cardinal was invited to prove the accusations moved against certain women from Lecco, charged with diabolical witchcraft, by verifying the corpus delicti [body of the crime] before sentencing them to be burned at the stake. A document the importance of which was recently underlined by historians, to whom the letter represents a milestone of change in the line taken by the Catholic Church in the matter of diabolical witchcraft, which was the origin of the famous Instructio pro formandis processibus [preliminary investigation for trials to be held]. For this discovery he is invited by the Academic Library and by the Faculty of Literature of the University of Pisa to the first international conference “Witchcraft and witches in modern Europe” (1994), where he gives a presentation on the controversy risen between [Cardinal] Borromeo and the Congregation of the Holy Office.

Still on the subject of persecution in Lombardy, in 1998-1999, he conducts research at the Archive of the Congregation of Doctrine and Faith (former Holy Office), which leads him to the discovery of certain unpublished documents on the persecution against witches in the ancient diocese of Como, documents that were [then] made public within the national convention “Witches, devils, and sibyls” (Como, 2001), organized by Prof. Cardini.

In 2004, together with the director of the National Archive of Alessandria, he is appointed by the City Council of Triora (province of Imperia) to organize the fourth national historical - anthropological conference on witchcraft, “The Western Way. Ancient traditions and witch hunt in the alpine cloister”, in which, for the first time, historians and anthropologists discuss the issues of the long duration of the hunt and the cultural and symbolical foundations of “diabolical witchcraft”.

After winning scholarships in 1992 at the Istitute of historical-philosophical studies in Naples, and in 1998 at the Institute of Renaissance studies of Ferrara, he continues his research activity on behalf of the Historical Society of Como, on the journal of which he has published a series of articles on the sources of the study of the Dominican Order in the ancient diocese of Como, referring in particular to the convent of St. Giovanni Pedemonte, where the local Inquisition court was held.

The research conducted in these years is characterized by the focus on that specific form of religious deviance in modern Europe which is labelled under the all-embracing term of “diabolical witchcraft”, on the world of victims, and on their values, symbols, beliefs and practices. From this perspective, his investigations are pointed not only towards the study of trial documents and written sources pertaining the history of prosecutors: Inquisition, Dominicans (in the ancient dioceses of Como and Milan), but also towards the search of testimonies coming from the folkloric tradition, trying to bridge the traditional gap between the historical approach and the anthropological one which persists in this field of study.

[While] collaborating with scientific journals and radio-television documentaries, in 1998 he founds, along with G. Lutzenkirchen, the Center of Historical-Anthropological Studies Alfonso M. Di Nola - Popular cults, cultures and medicine.

Since 2007 he presides over the CIRE (Center of Ethno-Historical Research), based in Como.