Do you ever wonder about St. Matthias and what he did before and after his one and only appearance in the Bible, when they cast lots and choose him as the replacement for Judas Iscariot in Acts 2? So does most of the world, as it turns out.
Regarding his life before his apostolate, we can assume he was among the 70 whom Jesus sent out because in Acts Peter says that Judas’ replacement must have been with them from the beginning. His Wikipedia entry cites Clement of Alexandria as saying that St. Matthias was possibly the same person as Zacchaeus (Lk. 19:1-10).
Some agreement surrounds his preaching enterprise beginning in Judaea (Wikipedia and abbamoses agree). This makes sense, since all of the apostolic activity began in Judaea before spreading throughout the known world. According to one tradition, poor St. Matthias was stoned to death in Jerusalem. Although not entirely unbelievable, there comes to be a certain sameness to the stories told about lesser-known apostolic characters, so this may be pious fiction. According to Hippolytus he died of old age in Jerusalem.
Another and more exciting tradition places him in Aethiopia following his stint in Judaea. Aethiopia most likely did not mean Ethiopia, though. Wikipedia says that Nicephorus thinks “Aethiopia” is actually “Colchis” on the Black Sea, now in Georgia (the famous destination of Jason and the Argonauts). The basis for this, I reckon, is the presence of his alleged remains there; although, if those are St. Matthias’ remains, then whose remains did St. Helena allegedly pick up? Regardless, I have no idea why someone would think that Aethiopia would be Colchis of all places. Aethiopia, speaking Hellenically, is the place of the burnt-faced people and is always south, usually south of Egypt and Libya, thus Nubia/Sudan/Ethiopia, but never north of Greece at Colchis.
Anyway, so St. Matthias brought the Gospel to Aethiopia, wherever that is. Not only is he in Aethiopia, he’s in the city of man-eaters in Aethiopia, in fact. The tradition that asserts the cannibals includes the apocryphal Acts of Andrew and Matthias, although the country is merely identified as “the country of the man-eaters” — perhaps Colchis? Are Georgians cannibalistic? (I don’t think so.) Said Acts are interesting because they are clearly related to the Old English poem Andreas (in OE here, in Mod English in the Everyman book Anglo-Saxon Poetry) in which St. Andrew the Apostle rescues St. Matthew from a city of cannibals in Mermedonia, not Aethiopia. In fact, most of the manuscripts say the Acts are of Andrew & Matthew, but the earliest says of Matthias (see CCEL).
St. Matthias (or St. Matthew or no one at all, given that anthropophagy is rare and the story is of dubious origin) was imprisoned by the man-eaters and lined up to be their next feast. He prayed for deliverance, and Jesus brought him St. Andrew on a ship (so maybe Colchis?). Andrew gets there, sneaks into the city, and finds Matthias sitting in his prison cell singing (ala Sts. Paul & Silas). Then the two apostles performed some miracles, culminating in Matthias being transported in a cloud along with Andrew’s disciples and showing up on a hill where Peter is preaching. Andrew stayed behind to perform a few more miracles, debate with the Devil, and convert the man-eaters.
The Acts do not tell us about what St. Matthias does next. At some point he died, possibly in Jerusalem, possibly in Georgia, possibly in Africa south of Egypt and Libya. It’s all rather vague, revealing the paucity of information we have about first-century Christianity outside of the New Testament.