In an interview prior to the start of the 1963 season, Baltimore manager Billy Hitchcock listed McNally among a group of prospects that could provide "whatever else is needed" for Baltimore's pitching staff. An injury to Dalkowski helped McNally make the team as a left-handed reliever. After one game out of the bullpen, he made an emergency start for an injured Chuck Estrada on April 20, limiting the Cleveland Indians to one run in a complete game, 7–1 victory. He won his first two starts, but after giving up seven runs and five runs in his next two, respectively, he was moved back to the bullpen, where he was used as a reliever through the beginning of June. Then, Estrada was placed on the disabled list on June 8 due to a bone spur and calcium deposits in his elbow. McNally replaced him in the rotation on June 12 and was used as a starter the rest of the year. He took a no decision on June 12 but held the New York Yankees to two runs (one earned) over innings in a 3–2 loss. On August 22, he threw a complete game against the California Angels, striking out eight while giving up one run in a 5–1 victory. In 29 games (20 starts) his rookie year, McNally had a 7–8 record, a 4.58 ERA, 78 strikeouts, 55 walks, and 133 hits allowed in innings pitched. Following the 1963 season, McNally furthered his development by pitching winter ball in Puerto Rico.