For the 1958 season, he was promoted to the Raleigh Capitals of the Class B Carolina League, where he posted a 9–6 record and a 3.09 earned run average.

He also saw time with the Class A Eastern League Allentown Red Sox, where he posted up a 9–4 record with a dominant 1.68 ERA.

[1] 1961 marked Stallard's first full season in Major League Baseball, starting in 14 games and playing in a relief role for 29.

In 62⁄3 innings pitched, Stallard gave up one earned run on six hits, but he would get a no decision as Boston reliever Arnold Earley blew a 1–0 lead which eventually led to a 4–3 loss to the Chicago White Sox.

[4] Stallard struck out five and gave up five hits and just the one earned run in seven innings on the outing, but the Red Sox failed to score in a 1–0 loss, dropping him to a final record of 2–7 for the season.

[1] Stallard appeared in only one game for the Red Sox in 1962,[1] spending the rest of the season with the minor league Class AAA Seattle Rainiers, where he threw for a 7–6 record and a 3.49 ERA.

Even with his abysmal record, Stallard was still tied for 2nd with Jack Fisher for the highest number of wins for the Mets, only one behind Al Jackson (11–16).

[1] Stallard also gained the unfortunate distinction, albeit less well-known, as the starting pitcher who lost in Jim Bunning's perfect game on June 21, giving up six earned runs in 5+2⁄3 innings.

[12] While with the Mets, Stallard developed something of a taste for New York's night life, dating, among others, actress Julie Newmar, who would go on to play Catwoman in the Batman television series.

On December 7, 1964, Stallard joined the St. Louis Cardinals in a move that sent him to the Cards in exchange for Johnny Lewis and Gordie Richardson.

[1] Stallard appeared as an imposter for country music singer Bill Anderson in the February 15, 1965 episode of To Tell the Truth.

[14] During the 1966 season, Stallard was very vocal about his displeasure of being assigned to the bullpen,[15] though he had a 6.10 ERA at the time and had just came off three consecutive games where he gave up one or more earned runs in relief.

Stallard played his final Major League game on July 24 against the Chicago Cubs on the front-end of a doubleheader.

[17] Soon after his final appearance, the Cardinals reassigned Stallard to the Class AAA Tulsa Oilers of the Pacific Coast League.