To speak in a very general way about the Middle Ages, the accusation of devil worshipping was usually used as an additional attack on a group that were already being accused of heresy, either for reasons of dogma or political motives.

I will concentrate on a two groups of the 12th century that were accused of worshipping the devil rather than looking at individuals who were accused. This is simply because there are literally hundreds of cases of people, particularly women being accused of worshipping Satan (1) and it is almost impossible to verify these individual cases because they do not have a power-system around then that can be adequately studied. If using these individuals as evidence and therefore the confessions they gave under torture or extreme mental stress, then the answer to your question would be yes, there were devil worshippers. However, these would not fit the “organised groups of Christian devil worshippers” which you are after.

When studying heretical groups of the Middle Ages it is vital to remember that nearly every single primary source we have was written by people that despised them. Take for example the Cathars. One of the most prominent heretical groups of the Middle Ages, the group that sparked the Albigensian Crusade, and led to the foundation of the Dominican order and later the inquisition.(2) We have one document that is widely accepted to be written by them, about them, that is the Cathar Council of St Felix, and even this is hotly debated amongst scholars. (3) The document is incredibly mundane and is mainly about the organisation of their church, such as the diocese of Cathar bishops. The point here is that any writings claiming that groups worshipped the devil are written by members of the Catholic Church, not the groups themselves.

The Cathars were accused of devil worshipping, as were the Waldensians a group of devout Christians who preached that people should follow in the example set by Christ and live as austere mendicants. (4) The Church condemned them as heretics, the irony here being that the Waldensians spent their time preaching against heretics. All of the people within these groups would not claim to be devil worshippers until they were either tortured or tricked into a confession. (5) Why would they lie about this when they were open about other aspects of their beliefs which were heretical?

Somebody may know of a group that I have not read about which were openly worshipping Satan but this is just an insight into some accused groups I have researched. Ultimately, like many subjects within the Middle Ages, the answer is we don’t know. However, devil worshipping appears to be a convenient and shocking accusation to make against a group that the Church or the Nobility do not like.

(1) P. G Maxwell-Stuart, Witch Beliefs and Witch Trials in the Middle Ages: Documents and Readings, 2011.

(2) M. Barber, The Cathars, 2nd edn, 2013.

(3) Bernard Hamilton, The Cathar Council of Saint-Félix Reconsidered. This remains, in my opinion the fairest take on the document, Hamilton concludes it is genuine, for the other side of the argument try anything by Mark Gregory Pegg’s article in Cathars in Question, edited by Antonio Sennis.

(4) J. Kolpacoff Deane, A History of Medieval Heresy and Inquisition, 2011. And G. Audisio, The Waldensian Dissent: Persecution and Survival, c.1170-c.1570, 1999.

(5) R. I. Moore, The Formation of a Persecuting Society: Authority and Deviance in Western Europe 950-1250.

The best selection of primary sources for heresy can be found in W. L. Wakefield and A. P. Evans, Heresies of the High Middle Ages, 1969. You’ll have to scout through it for references to devil worshipping but I think you will see that it was really a sort of bonus accusation to make to seal the deal on public condemnation of distrustful movements.