He played in Major League Baseball as a right-handed pitcher from 1961 through 1972 for the Milwaukee / Atlanta Braves, Cincinnati Reds and the St. Louis Cardinals.

Cloninger used a bat of teammate Denis Menke to hit both home runs, and they stood as the only two grand slams of his major league career.

He was acquired along with Clay Carroll and Woody Woodward by the Reds from the Atlanta Braves for Milt Pappas, Bob Johnson and Ted Davidson on June 11, 1968.

In 2002, he became the pitching coach for the Boston Red Sox, but was forced to step down in early 2003 when he underwent successful treatment for bladder cancer that had been diagnosed in spring training.

At one point, Cloninger, age 61 at the time but not shying away from trouble, grabbed Orioles player Brook Fordyce in a headlock.