A two-time All-Star player, Stuart was notable for being an integral member of the 1960 Pittsburgh Pirates team which upset the New York Yankees to win the 1960 World Series and, for being the 1963 American League RBI champion.

Stuart threw and batted right-handed; during his playing days, he stood 6 feet 4 inches (1.93 m) tall, weighing 212 pounds (96 kg).

After initially sputtering upon his return to professional baseball in 1955, Stuart set a Western League record with 66 home runs in 1956 with the Lincoln Chiefs.

[6] Stuart clubbed 31 home runs in 80 games for the Salt Lake City Bees when he received his call to the majors in July.

Fueled by an MVP season from shortstop Dick Groat, and the emergence of young star Roberto Clemente, the 1960 Pirates sailed to the NL pennant by seven games over the Milwaukee Braves.

In their 1960 World Series victory over the New York Yankees, Stuart was held to three singles in twenty at bats with no RBIs or runs scored.

[9] Stuart was in the on deck circle as a pinch hitter when Bill Mazeroski hit the ninth-inning home run off Ralph Terry that won the World Series.

After the season, Stuart and pitcher Jack Lamabe were traded to the Boston Red Sox for Jim Pagliaroni and Don Schwall.

[14] Endearing him even more to Bosox fans was the fact that through the first 26 games of the 1963 season, Stuart had five home runs and seventeen RBIs without committing an error.

[15][16] His .253 batting average, seventeen home runs and fifty RBIs at the All-Star break earned him a second-place finish to the Yankees' Joe Pepitone in fan balloting, but he was left off the team by American League manager Ralph Houk.

[20] Despite his well-documented defensive struggles, on June 28, Stuart became the initial first-baseman in major league history to record three assists in one inning.

On October 27, 1965 the Phillies acquired Gold Glove first baseman Bill White, Bob Uecker and Stuart's former Pirates teammate Dick Groat from the St. Louis Cardinals for Pat Corrales, Alex Johnson and Art Mahaffey.

Four months later, Stuart was traded to the New York Mets for minor leaguers Wayne Graham, Bobby Klaus and Jimmie Schaffer.

[24] The Mets moved 21 year old All-Star Ed Kranepool into a left field platoon with Ron Swoboda in order to make room for Stuart at first base.

However, once Kranepool demonstrated he was a terrible left fielder, and Stuart committed six errors by June 5, that disastrous idea was abandoned.

In January 1973, almost four years after Stuart's retirement, it was noted that the not yet instituted designated hitter rule "would have suited Dr. Strangeglove perfectly".