Matthias was chosen to become the 12th Apostle after the death of Judas. In Acts, chapter 1, Peter explains to about 120 followers the need to replace Judas, as he recites a Psalm of David that states "Let his work be given to someone else to do," in reference to Judas.
Two men are nominated by the assembly, Joseph Justus, who was also called Barsabbas, and Matthias. The assembly prayed to God to make the right choice, and Matthias was chosen. Nothing more is written of him in the Bible.
Tradition states he was one of the 70 sent out by Jesus in Luke 10:1, that he preached in Judea, and that he died a martyr. Matthias means "Gift of God."