

Sine none of Joseph's and Mary's other sons believed in Jesus during his pre-crucifixion ministry (John 7:5), it is very plausible that James led some (or all) of his brothers to faith in Christ after his own conversion. Though their mother's belief was apparently decisive, the transformation in their brother, James, may have been. The mention of 'brothers' (plural) in Acts 1:14 in the Upper Room requires the conversion of at least two of Jesus' half-brothers. Almost certainly included would be James and Jude (Matt. 13:55; Jude 1), the brothers who contributed books to the New Testament.
The next mention of James is in Acts 12:17, after Peter was miraculously freed from prison by an angel (verses 3-17). Peter asked those gathered for prayer to get word of what had happened to 'James and the brothers'. 'Brothers' almost certainly means the wider church in Jerusalem, thus the mention of James' name probably reflects his recognized leadership role in the church.
Two other inclusions of James' name in Acts underline his prominence as a leader in the Jerusalem church. At the Jerusalem Council, James was the last leader to speak, adding Biblical support to the testimony of Peter (Acts 15:7-11) and Barnabas and Paul (verse 12). Since James' approach was essentially accepted word-for-word by the other leaders and the gathered church (verses 13-29), he must have commanded great respect from all.
The final mention of James in Acts is at the conclusion of Paul's third missionary journey. When Paul arrived in Jerusalem, he went to James and 'all the elders were present' (Acts 21:18). This wording again indicates that James was a leader of even higher station than the elders. Since the other apostles besides Paul were not referred to in Jerusalem in the book of Acts after the Jerusalem Council, the likelihood that James was, in effect, the ranking Christian leader in Jerusalem from that time forward until his death is fairly strong.
Most of the remaining references to James in the New Testament outside of Acts seem to fit into the time frame of the appearances of James in Acts. Probably the earliest of these are in Galatians, which most likely was written not long before the Jerusalem Council. In Gal. 2:9 James, Peter and John are termed 'pillars' of the church. Paul's interaction with those leaders in Jerusalem was very positive, as they recognized his mission to the Gentiles (verse 9). However, at a later point, men claiming the authority of James came to Syrian Antioch and caused great dissension in that primarily Gentile church (verse 12). Since the visitors even managed to persuade Peter and Barnabas to assume certain legalistic practices (verses 12-13), it is likely that the assumed influence of James was part of the Judaizers' revenge.
In 1 Cor. 9 Paul noted that 'the Lord's brothers' were married (verse 5) and that their families were supported by the church financially (verses 4-6). Surely James would be included in that phrase. The reference in 1 Cor. 15:7 to the appearance of the resurrected Christ to James is proof of that prominence
The Epistle of James was almost certainly written by James, who grew up in the same household as Jesus, although he does not make mention of that relationship, but instead humbly calls himself 'a servant of God and of the Lord Jesus Christ' (James 1:1). The reference to the Old Testament, Christ's Sermon on the Mount, and prayer (James 4:2-3, 5:13-16) fit well both the scriptual picture and the strong extra-biblical tradition about James. Because the congregation of believers is called both 'synagogue' (James 2:2) and ecclesia ('church', James 5:14), the epistle may be one of the earliest New Testament writings, dating from a time in which the church in Jerusalem was still more of a messianic synagogue within Judaism than a clearly distinct religious grouping.
The final reference to James in the New Testament is in the first verse of the short Epistle of Jude, Jude, like James, calls himself 'a servant of Jesus Christ', but also goes on to bolster his authority as a writer of Scripture by the further description 'a brother of James' (verse 1). By that point in the apostolic era, the only James that could be named without further description is the Lord's younger half-brother.
Tradition holds that James was killed for his faith in the early 60s AD by the Jews. He is said to have been thrown from the roof of the Temple in Jerusalem, though this is not certain. The developing church lost a great leader and godly example when James died.
From: "The Complete Who's Who in the Bible," Paul D. Gardner, Editor (1995)