Before the 1959 season, Gregory was signed by the St. Louis Cardinals. He spent time in the minors, was released, and before the 1964 season was signed by the Cubs. On April 17, 1964 he made his big league debut at the age of 25 wearing number 28. In 11 games, he pitched 18 innings for a 3.50 ERA. He did not have a decision. He was also used as a pinch hitter. In 13 at-bats, he collected 1 hit for a .077 average. Gregory played his final game on September 11, 1964.
Gregory currently resides in Fresno, California.