Atwell, listed at 5 feet 9 inches (1.75 m) tall and 185 pounds (84 kg), batted left-handed and threw right-handed.

He was born in Leesburg, Virginia, and served in the United States military during World War II.

A strong defensive catcher, he shortened his career when he hurt his knee sliding while playing for the Triple-A Montreal Royals during the 1949 International League season.

His most productive campaign came in his rookie year with the 1952 Cubs, when he posted career-highs in batting average (.290), RBI (31), runs (36), hits (105), doubles (16), games played (107), and was selected to the National League All-Star team.

In 1953 he was part of a ten-player, early-June trade that saw the Cubs acquire Baseball Hall of Fame slugger Ralph Kiner from the Pittsburgh Pirates.