The right-handed pitcher played all or part of seven seasons in Major League Baseball spread over 15 years (between 1945 and 1959) for the Boston Braves, Pittsburgh Pirates, Washington Senators and Chicago Cubs.

His professional career spanned 24 seasons, from 1940 until 1963, missing only 1944 due to voluntary retirement during World War II.

Singleton worked in 145 games pitched in the big leagues, including 19 as a starter, putting up a record of 11–17 and earned run average of 4.83.

He also was part of a notable trade on September 30, 1946, when he was shipped by the Braves to the Pirates in a six-player deal that brought third baseman Bob Elliott to Boston.

Elliott would be chosen winner of the National League's 1947 Most Valuable Player Award and lead the Braves to the 1948 NL pennant.