A “bonus baby,” Sadecki won Cardinal Rookie of the Year honors after posting a 9–9 record as a 19-year-old in 1960. He became a full-time starter in 1961, posting a 14–10 record. However, he exhibited periods of wildness during his first two seasons, walking 86 batters in his rookie season (in 157 1⁄3 innings pitched) and 102 in 1961.
Sadecki’s best season was 1964; he posted a 20–11 record and, along with Bob Gibson and Curt Simmons, helped pitch the Cardinals to the National League pennant, their first since 1946, with the Philadelphia Phillies and Cincinnati Reds finishing tied for second, one game behind the Redbirds. The Phillies had held a 6 1⁄2-game lead over the Reds and Cardinals on September 20 with 12 games to play, only to squander the pennant by losing ten consecutive games, while the Cardinals and Reds recorded winning streaks of eight and nine games respectively. Sadecki won his 20th game on September 29 against the Phillies for Philadelphia’s ninth consecutive loss and St. Louis’ seventh consecutive win. The win also pulled the Cardinals even with the Reds who, after taking over first place on September 27, had their nine-game winning streak snapped by the Pittsburgh Pirates on Bob Friend’s 2–0 shutout earlier in the day. The next day, the Cardinals took over first place by defeating the Phillies while the Reds were again shut out by the Pirates.
The Cardinals, ahead by a half-game over the Reds entering the final weekend, now appeared to have the pennant put away: their final three games were at home against the lowly New York Mets, while the Phillies and Reds were to play a two-game series at Crosley Field. However, the Cardinals lost the first two games of the series, first with Al Jackson outduelling Gibson 1–0 (that same day, the Phillies spotted the Reds a 3–0 lead, then scored four runs in the eighth inning to win 4–3 and finally snap their 10-game losing streak), then Sadecki getting battered in one inning, giving up five runs in a 15–5 loss. The Cardinals won the pennant on the final day, defeating the Mets 11–5 while the Phillies hammered the Reds 10–0.
After unexpectedly winning the pennant, the Cardinals defeated the New York Yankees in the World Series. Sadecki started Game One and gave up three runs in the second inning, but settled down after that and defeated the Yankees 9–5, in what would be Whitey Ford’s final World Series game. Starting Game Four, Sadecki was again battered early, this time being pulled after giving up three runs in one-third of an inning. The Cardinals, however, came back to win 4–3, the runs coming on Ken Boyer’s sixth-inning grand slam. The Cardinals went on to win the Series, with Gibson winning Games Five and Seven.
In 1965 Sadecki’s record plummeted to 6–15, and his earned run average skyrocketed to 5.21. On May 8, 1966 he was traded to the San Francisco Giants for Orlando Cepeda. In 1967 he went 12–6 with a career-best 2.78 ERA; in 1968 he posted a 2.91 ERA but with a 12–18 record, the 18 losses tying him with Claude Osteen for the Major League lead. After a 5–8 record as a spot starter in 1969 Sadecki was again traded, this time to the New York Mets.
In 1973 Sadecki pitched for the Mets’ National League champions who, like the 1964 Cardinals before them, unexpectedly won the pennant, trailing by as many as nine games behind the Chicago Cubs and winning the National League East title on the final weekend. (Coincidentally, four years earlier the Mets, prior to unexpectedly winning the World Series, had also won the division title by jumping past the Cubs.) Sadecki pitched as a “swingman”—relief pitcher and spot starter in a rotation with Tom Seaver, Jerry Koosman and Jon Matlack—in helping the Mets win the division. He pitched four of the seven games of the World Series, which the Mets lost to the Oakland Athletics, gaining the save in Game Four.
In his 18-year career, Sadecki won 135 games against 131 losses, with a 3.78 ERA and 1614 strikeouts in 2500⅔ innings pitched.
When Catholic Charities of Kansas City and the Baseball Tomorrow Fund renovated a baseball field in 2002, it was dedicated and renamed Ray Sadecki Field in honor of the neighborhood native. It stands at 9th and Homer Streets in Kansas City, Kansas.
On June 14, 2007 Sadecki was inducted into The National Polish-American Sports Hall of Fame.
Sadecki died from complications of blood cancer on November 17, 2014.