James the brother of Jesus, later known as "James the Just," was an important figure in Jerusalem in the early decades of the church's history. According to Paul, James was not only an "apostle" but one of only three respected as the "backbone" of the community in Jerusalem. In fact, James is listed first of the three (Galatians 1:19; 2:9). In the same passage, Paul says that "James sent some Jewish followers" to Antioch (Galatians 2:12, CEV). Elsewhere, he lists James among those who had an (individual) encounter with Jesus after his resurrection (1 Corinthians 15:7). Similarly, in Acts, James emerges as the primary leader of the community in Jerusalem. When the apostles and other leaders meet to decide whether Gentiles ought to be circumcised, James gives his opinion and the community ratifies it (see Acts 15:13-29). Later in Acts, Paul makes it a priority to meet with James in Jerusalem (21:18). Finally, a saying in the extrabiblical Gospel of Thomas (12) honors "James the Just" as the one who will lead the disciples after Jesus' departure.

Josephus, a first-century Jewish historian, also mentions James as "the brother of Jesus, who was called Christ." Josephus reports that the high priest and the Jewish council condemned James and some others to stoning. They were charged with breaking the Law of Moses. This decision was unpopular with law-keeping Jews (perhaps the Pharisees), and it led to the high priest losing his office (Antiquities of the Jews 20.9.1). This event would have occurred in the year 62—about 30 years after Jesus' crucifixion. Josephus's account agrees with Paul and Acts in portraying James as a leader in Jerusalem and as a person who kept the Law of Moses scrupulously. A second-century Christian historian claims that James was also a Nazirite (a man consecrated from birth, who does not shave or drink wine).

In 2002, an ossuary (a stone box for preserving human bones) came to public attention and aroused much excitement. An inscription on the ossuary reads, "James, son of Joseph, brother of Jesus." Some archaeologists believe that this ossuary provides firm historical evidence for the existence of both Jesus and his famous brother. Others point out that this could be another "James" (there were probably many men of that name with fathers named "Joseph" and brothers named "Jesus"). Still others argue that the second half of the inscription ("brother of Jesus") is a later, forged addition. In any case, historians are convinced both that James the brother of Jesus was a historical person, and that he died and was buried in Jerusalem.

Finally, since ancient times some have believed that James the Just penned the New Testament's letter of James, while others have believed that someone else did. The document itself claims only to be written by someone named "James" (James 1:1). Current academic biblical scholarship favors another author, although some conservative scholars continue to view it as a letter by this famous brother of Jesus.