OF/1B Stan Musial (1941-1963) - 22 years
Stan Musial is the best player to ever play for the St. Louis Cardinals, and he spent his entire 22-year career with the Cardinals. Musial accumulated 128.5 bWAR during his career. He was the National League's Most Valuable Player three different years, he went to 24 All-Star Games, and he won the National League batting title seven different times. Musial was inducted as a player to the National Baseball Hall of Fame in 1969.
Stan Musial's Baseball Reference page is littered with bold and italic stats, meaning he led the National League and all of baseball several times during his career. Add to the fact that Stan served his country in 1945, and you have one of the best players and men of his generation. He was even given the Presidential Medal of Freedom, the highest civilian honor in the United States, by former President Barack Obama in 2011.
LHP Al Brazle (1943-1954) - 10 years
Al Brazle was a part of "The Greatest Generation" in America. He was born in 1913, and he made his major-league debut on July 25th, 1943 with the Cardinals at age 29. After his rookie year in 1943, Brazle joined the military for two years, and he didn't play in 1944 or 1945.
In his 10 years with the Cardinals, Brazle accumulated 21.4 bWAR. He finished his career with a 97-64 record, a 3.31 ERA, and 47 complete games. In 1954, Brazle was the oldest player to appear in a National League game at the age of 40.
RHP Bob Gibson (1959-1975) - 17 years
Bob Gibson is the best pitcher to have ever played for the St. Louis Cardinals. In his 17-year career, Gibson was a nine-time All-Star, a nine-time Gold Glove recipient, a two-time Cy Young Award winner, an MVP, and a two-time World Series champion. In 1981, Gibson was inducted into the National Baseball Hall of Fame, and he was an inaugural member of the St. Louis Cardinals Hall of Fame in 2014.
Gibson had a career 251-174 record and a 2.91 ERA in 3,884.1 innings. He struck out 3,117 batters, and his 1.12 ERA was the best in baseball in 1968. 255 of Gibson's 482 starts were complete games, and he tossed 56 shutouts during his career. Few if any pitchers were better than Gibson was, and he's worthy to be known as one of baseball's best to have ever played the game.