Andrew and his brother Peter were fishermen by trade, hence the tradition that Jesus called them to be his disciples by saying that he will make them "fishers of men" (Greek: ἁλιεῖς ἀνθρώπων, halieis anthrōpōn). At the beginning of Jesus' public life, they were said to have occupied the same house at Capernaum.
In the Gospel of Matthew (Matt 4:18–22) and in the Gospel of Mark (Mark 1:16–20) Simon Peter and Andrew were both called together to become disciples of Jesus and "fishers of men". These narratives record that Jesus was walking along the shore of the Sea of Galilee, observed Simon and Andrew fishing, and called them to discipleship.
In the parallel incident in the Gospel of Luke (Luke 5:1–11) Andrew is not named, nor is reference made to Simon having a brother. In this narrative, Jesus initially used a boat, solely described as being Simon's, as a platform for preaching to the multitudes on the shore and then to achieving a huge trawl of fish on a night which had hitherto proved fruitless. The narrative indicates that Simon was not the only fisherman in the boat (they signaled to their partners in the other boat … (Luke 5:7)) but it is not until the next chapter (Luke 6:14) that Andrew is named as Simon's brother. However, it is generally understood that Andrew was fishing with Simon on the night in question.
In contrast, the Gospel of John (John 1:35–42) states that Andrew was a disciple of John the Baptist, whose testimony first led him, and another unnamed disciple of John the Baptist, to follow Jesus. Andrew at once recognized Jesus as the Messiah and hastened to introduce him to his brother. The Byzantine Church honors him with the name Protokletos, which means "the first called". Thenceforth, the two brothers were disciples of Christ. On a subsequent occasion, prior to the final call to the apostolate, they were called to a closer companionship, and then they left all things to follow Jesus.