Marion played with the St. Louis Cardinals between 1940 and 1950. He took over managerial duties in 1951, and joined the St.Louis Browns as a player-manager in 1952, roles he would embrace until 1953. At the end of the 1954 season he managed the Chicago White Sox, until his retirement in 1956.

In a 13-season career, Marion posted a .263 batting average with 36 home runs and 624 RBI in 1572 games. He made eight consecutive All-Star Game appearances (1943-50) and in 1944 he earned National League MVP honors. As a manager, he compiled a 356-372 record.

As a shortstop, Marion was synonymous with St. Louis baseball until the appearance of Ozzie Smith. It's clear that Marion wasn't flashy as Smith, but at 6 ft 2 in and 170 pounds (77 kg), he disproved the theory that shortstops had to be small men. He brought the same grace to his position that Fred Astaire and Gene Kelly brought to the stage and films. Nicknamed "Slats", Marion had unusually long arms which reached for grounders like tentacles, prompting sportwriters to call him "The Octopus".

From 1940-50, Marion led the National League shortstops in fielding percentage four times during his reign as the glue of the Cardinals infield, despite several players moved around the infield during these years. If Gold Glove Awards had been awarded during his career, Marion would have earned his share. In 1941 he played all 155 games at shortstop (also a league-high) and in 1947 he made only 15 errors for a consistent .981 percentage.

Beside this, Marion was a better-than-average hitter for a shortstop. His most productive season came in 1942, when he hit .276 with a league-lead 38 doubles. In the 1942 World Series, one of four series in which he participated with the Cardinals, he helped his team to a World Championship with his amazing glove. In 1943 he batted a career-high .280 in the regular season and hit .357 in the 1943 World Series, which was more than respectable considering his value in the infield.

In 1951 Marion managed the Cardinals and was replaced by Eddie Stanky at the end of the season. Then, he moved across the town to the Browns, and took over for manager Rogers Hornsby early in 1952. Marion was named by the Browns as their player-manager, and was let go in 1953. He also managed the White Sox for two-plus years (1954-56), retiring at the end of the 1956 season.

Beginning 2005, according Official St. Louis Cardinals Historian Erv Fischer, Don Gutteridge is the oldest living former Cardinals player. He will be 93 in month of June. Next in the order is Marion, at 87, Stan Musial, at 84, and Red Schoendienst, at 81.