Pappas was born in Detroit, Michigan to Greek parents, and his birth name was Miltiades Stergios Papastergios. In , as a senior at Cooley High School, Pappas was scouted by several teams and signed with the Orioles at the suggestion of Hal Newhouser, a former star pitcher for the Detroit Tigers who lived in the Detroit area. Pappas signed for $4,000 and pitched only three games in the minor leagues before being called up in August. He made his Major League debut on August 10 in relief against the New York Yankees. In he made the Orioles’ starting rotation and began a streak of 11 consecutive double-digit win seasons with a 10–10 record.