He was converted by Thaddeus of Edessa, also known as "Addai"), and is said to have had as his spiritual director, Mar Aggai.

[2] According to the Acts of Mari, Addai sent him to convert the area south and east of Edessa.

Mari is believed to have done missionary work around Nineveh, Nisibis, and along the Euphrates, and is said to have been one of the great apostles to Syria and Persia.

[3] He performs a number of miracles as proof of his holiness.

His feast day is 5 August in the Christian calendar.