Butler grew up near Forbes Field in Pittsburgh, Pennsylvania. Butler attended Mt. Carmel College High School in Niagara Falls, Ontario. His good friend and neighbor, Frank Thomas of Pittsburgh Pirates and baseball fame also attended Mt. Carmel and St. Bonaventure University with Butler. Both gave up the seminary to play professional sports.
At St. Bonaventure, Butler was coached by Joe Bach, who coached the Steelers from 1935–1936 and 1952-1953. Butler played both offensive end and defensive end in college.
Butler was an undrafted free agent whom the Pittsburgh Steelers brought onto their roster in 1951 out of St. Bonaventure. Butler became a defensive back and occasional wide receiver for the Steelers.
As a rookie, Butler intercepted five passes for 142 yards. In 1953, he had nine interceptions and returned two of them for touchdowns. In 1957, he led the league in interceptions with ten, four of which came in a game against the Washington Redskins on December 13, 1953. One of the interceptions resulted in a 35-yard return for a touchdown to win the game for the Steelers 14-13. It tied a record. The following year Butler set a record with two interception returns for touchdowns and a career-best 10 interceptions.
Offensively, Butler scored a touchdown against the New York Giants. It was late in the game and Butler had caught the game winning touchdown pass from Jim Finks.
In 1958, Butler added nine more interceptions to his growing list. During the 1959 season after garnering two interceptions, Butler was forced to retire due to a leg injury he received when tight end Pete Retzlaff of the Philadelphia Eagles rolled into Butler's knee.
Butler never made more than around $12,000 as a player with the Steelers. Following his playing career, Butler spent 46 years with the BLESTO Scouting Combine (44 as its' director). During this time, his contributions to the NFL included scouting and evaluating over 75,000 college athletes and starting the Combine scouting process that is still in use today.
Butler was named to four straight Pro Bowls from 1956–1959. He had 52 interceptions during his career and 865 yards. At the time of his retirement, Jack ranked second in career interceptions, behind only Hall of Famer Emlen Tunnell.
In October 2008, Butler was named as one of the 33 Greatest Pittsburgh Steelers of all-time. The Steelers named players to this team as part of their 75th anniversary season celebration. He was named to the National Football League 1950s All-Decade Team. He was named as a senior nominee for the Pro Football Hall of Fame for 2012 and was elected as a member on February 4, 2012.