As with James son of Alphaeus, there’s not much we can say about Jude of James without assuming he’s the same person as another Jude. It’s true that Jesus had a brother named Jude (Matthew 13:55, Mark 6:3). And the “of James” Luke uses to distinguish him from Judas Iscariot could mean he’s James’ brother, and Jesus had a brother named James. Plus, Jude who claims to have written the Epistle of Jude says he has a brother named James (Jude 1).
But John 7:3-5 may suggest Jesus’ brother Jude didn’t believe he was who he said he was until later, and at this point, Jesus had already called his disciples:
“Jesus’ brothers said to him, ‘Leave Galilee and go to Judea, so that your disciples there may see the works you do. No one who wants to become a public figure acts in secret. Since you are doing these things, show yourself to the world.’ For even his own brothers did not believe in him.” —John 7:3–5 (emphasis added)
John doesn’t say all of Jesus’ brothers didn’t believe in him, but this could be a signal that Jesus’ brother Jude wasn’t one of his 12 main disciples.
Additionally, the description in Luke 6:16 and Acts 1:13 which often gets translated as “son of James” is actually ambiguous. “Of James” is a more literal translation, and some scholars think it more likely means “son of James” than “brother of James.” Especially since Luke uses a form of the Greek word adelphos (brother) to communicate the relationship between Peter and Andrew (Luke 6:14) and he doesn’t place them next to each other as you’d expect him to do.
Jude AKA Thaddeus
In two of the lists of apostles, Jude appears to be referred to as Thaddeus (Matthew 10:2-4, Mark 3:16–19). Since these two names appear in about the same place in the lists, and the other names are consistent, church tradition (and most modern scholars) have always assumed Thaddeus was a nickname for Jude of James.
Since the name Judas had such strong negative associations in the early church, it wouldn’t be surprising if Jude preferred to go by another name, or if Matthew and Mark used the nickname to avoid confusion. (Thanks for nothing, guys.)
Did Jude the apostle write the Epistle of Jude?
Most traditions assume Jude the apostle wrote the Epistle of Jude because they assume he’s the same person as Jesus’ brother Jude. But unfortunately, Jude was a super common name, and this relies on assumptions. Today’s scholars have mixed opinions on Jude’s authorship.