The first baseman appeared in 122 games over all or parts of four major league seasons between 1953 and 1956 for the St. Louis Browns/Baltimore Orioles, Brooklyn Dodgers and Chicago Cubs.

Kellert threw and batted right-handed, and was listed at 6 feet, 21⁄2 inches (1.89 m) tall and 185 pounds (84 kg).

[1] Making his MLB debut at age 28 for the Browns on April 18, 1953, he was sent back to Oklahoma City after only two games.

He remained with the Dodgers all season, played in 39 games, and made 17 starts at first base when All-Star and Gold Glover Gil Hodges briefly switched to the outfield in early June and late August.

A week after the Dodger championship, Kellert was placed on waivers and claimed by the Cubs, where he spent the 1956 season but hit only .186 as a part-time first baseman.