Eric Aniva, 45, was prosecuted on the orders of President Peter Mutharika after publicly speaking about his role as a "hyena" in a BBC radio documentary earlier this year.
Aniva had told the BBC that he had slept with at least 104 women and girls, some as young as 12, in a ritual that lasts three days.He said each family paid him a fee of between $4 and $7.
In the first case of its kind, Aniva was found guilty on two charges on Friday after a one-day trial.
Custom in some parts of southern Malawi demands that a man, known as a "hyena", is paid to have sex with bereaved widows to exorcise evil spirits and to prevent other deaths occurring.At the request of a girl's parents, the "hyena" is also paid to have sex with adolescent girls to mark their passage to womanhood after their first menstruation.
Aniva, who pleaded not guilty, told AFP immediately after the sentence:
"I am disappointed because I thought I would be given a suspended sentence."The ritual, which many Malawians say is rarely practised today, is believed to also train girls to become good wives and protect them from disease or misfortune that could fall on their families.