Kellner, 6 feet (1.8 metres) tall and weighing 200 pounds (91 kg) during his career, batted and threw right-handed.

He started out with Lincoln in the Western League, winning three games and losing fourteen in his first pro season.

He served in the military in 1951 and part of 1952, but returned to baseball late in 1952 and debuted with Philadelphia on September 6 of that year.

In his very first game, he picked up a save, facing 19 batters over four innings pitched and giving up four hits and three runs.

His paternal great-grandfather, Johann Justus Kellner, a German immigrant, had arrived in central Texas in 1845.