The evangelist, was a Gentile. The date and circumstances of his conversion are unknown. According to his own statement (Luke 1:2), he was not an "eye-witness and minister of the word from the beginning." It is probable that he was a physician in Troas, and was there converted by Paul, to whom he attached himself. He accompanied him to Philippi, but did not there share his imprisonment, nor did he accompany him further after his release in his missionary journey at this time (Acts 17:1). On Paul's third visit to Philippi (20:5, 6) we again meet with Luke, who probably had spent all the intervening time in that city, a period of seven or eight years. From this time Luke was Paul's constant companion during his journey to Jerusalem (20:6-21:18). He again disappears from view during Paul's imprisonment at Jerusalem and Caesarea, and only reappears when Paul sets out for Rome (27:1), whither he accompanies him (28:2, 12-16), and where he remains with him till the close of his first imprisonment (Philemon 1:24; Col. 4:14). The last notice of the "beloved physician" is in 2 Tim. 4:11.
There are many passages in Paul's epistles, as well as in the writings of Luke, which show the extent and accuracy of his medical knowledge.