In the New Testament, Matthias replaced Judas Iscariot among the Twelve apostles.
Acts 1:15–26 describes the disciples gathering in Jerusalem after Judas’s death. Peter said that a replacement should be chosen from men who had accompanied Jesus from his baptism until the ascension. Two candidates were proposed: Joseph called Barsabbas, also known as Justus, and Matthias.
The gathered believers prayed and then cast lots. The lot fell to Matthias, who was counted with the eleven remaining apostles. This account appears only in Acts, and the New Testament gives no later narrative about Matthias’s missionary activity or death.
Matthias should not be confused with Paul, Barnabas, or other prominent early Christian leaders. Paul became an apostle in a different sense and was not selected in this particular replacement process. The episode also occurs before Pentecost in Acts, when the disciples were still awaiting the promised coming of the Holy Spirit.