He called himself a slave of his half-brother Jesus who he identified as Lord, Master, and Christ (Jude 1, 4). He had an eagerness to speak of salvation in Him (Jude 3) and readily warned the church about false teachers (Jude 4–16).
What follows below is an attempt to piece together the life of Jude as told by the Bible, using what few references to him that we have.
Jude grew up with Jesus and his other siblings in the house of Joseph and Mary and thus enjoyed being from the line of David. Being last in the list of four brothers (Matt 13:55), he may have been the youngest of them all, with sisters (at least two) scattered somewhere in the lineup.
In the book that bears his name, assuming this Jude was indeed its author, we see that he identified himself as the “brother of James” (Jude 1), who, as this was a notable James, must have been the leader of the early Jerusalem church (cf. Acts 12:17; 15:13; 21:18).
Both James and Jude (and Joses and Simon) were the biological half-brothers (or more simply, “brothers”) of Jesus, the most natural reading of the text (Matt 13:55). They were neither the cousins of Jesus as Roman Catholicism believes nor stepbrothers from Joseph’s supposed previous marriage as Eastern Orthodoxy believes, both theories stemming from the erroneous notion of the perpetual virginity of Mary.
Jude likely learned to be a carpenter like his father Joseph. Maybe he was old enough to notice when Joseph and Mary were looking for the twelve-year-old Jesus (Luke 2:41–52).