Matthias was chosen as an apostle to take the place of Judas of Kerioth after his betrayal.  It is believed that Matthias was one of the "Seventy" disciples sent out by Jesus (Luke 10:1), however, this cannot be proven.

He, along with the apostles Jude (Thaddaeus), Bartholomew, Simon the Zealot and Andrew are credited by Armenian tradition as the apostles who evangelized Armenia (great peril befell him in the cities of Colchis, Sebastopol and elsewhere.)