The Story of Matthias
Matthias appears in the New Testament in a single passage: Acts 1:15-26. The scene is Jerusalem, sometime between the ascension of Jesus and the day of Pentecost. About one hundred and twenty disciples are gathered. Peter stands and addresses them.
Peter's argument proceeds in two steps. First, he cites Psalm 69:25 and Psalm 109:8 to establish that Judas's defection and the vacancy it created were anticipated in scripture: "Let another take his office." Second, he sets the criteria for a replacement: the new apostle must have been with the community from the baptism of John through the day of the ascension, and must be a witness to the resurrection. Two men are put forward: Joseph called Barsabbas, also known as Justus, and Matthias.
The community prays: "Lord, you know everyone's heart. Show us which of these two you have chosen to take over this apostolic ministry, which Judas left to go where he belongs." Then they cast lots. The lot falls to Matthias, and he is added to the eleven apostles.
That is the entirety of what the New Testament records about Matthias. He is not mentioned again. The traditions that follow, missions to Ethiopia, Georgia, and Judea, martyrdom by axe or by stoning, are attested only in later and often conflicting sources. They may be true. They cannot be verified. Matthias went where he went. The text does not follow him.