The Book of Daniel mentions two archangels: Michael and Gabriel. In this Old Testament book, St. Gabriel interprets Daniel’s visions.
However, St. Gabriel is best known for his role in the New Testament. Zechariah, a Jewish priest, and his wife Elizabeth had been unable to have children, and Elizabeth was well beyond childbearing years. St. Gabriel approached Zechariah while the priest was burning incense in the temple. The angel said, “Do not be afraid, Zechariah, for your prayer is heard, and your wife Elizabeth will bear you a son, and you shall call his name John” (Luke 1:13). However, Zechariah doubted his words. In response, the archangel said, “I am Gabriel, who stand in the presence of God; and I was sent to speak to you, and to bring you this good news. And behold, you will be silent and unable to speak until the day that these things come to pass, because you did not believe my words, which will be fulfilled in their time” (Luke 1:19-20). This child who was born to Zechariah and Elizabeth was St. John the Baptist.
St. Gabriel also appeared to Mary at the Annunciation:
In the sixth month the angel Gabriel was sent from God to a city of Galilee named Nazareth, to a virgin betrothed to a man whose name was Joseph, of the house of David; and the virgin’s name was Mary. And he came to her and said, “Hail, full of grace, the Lord is with you!” But she was greatly troubled at the saying, and considered in her mind what sort of greeting this might be. And the angel said to her, “Do not be afraid, Mary, for you have found favor with God. And behold, you will conceive in your womb and bear a son, and you shall call his name Jesus.
He will be great, and will be called the Son of the Most High; and the Lord God will give to him the throne of his father David, and he will reign over the house of Jacob for ever; and of his kingdom there will be no end.”
And Mary said to the angel, “How can this be, since I have no husband?” And the angel said to her,
“The Holy Spirit will come upon you, and the power of the Most High will overshadow you; therefore the child to be born will be called holy, the Son of God. And behold, your kinswoman Elizabeth in her old age has also conceived a son; and this is the sixth month with her who was called barren. For with God nothing will be impossible.” And Mary said, “Behold, I am the handmaid of the Lord; let it be to me according to your word.” And the angel departed from her (Luke 1:26-38).