Selected in the sixth round of the 1958 NFL Draft by Green Bay, Ken Gray faced tough competition in a deep roster, playing alongside future Hall of Famers. Unable to secure a permanent spot with the Packers, the Texas native was claimed by the Chicago Cardinals, making his debut as a defensive end in his rookie year. However, this defensive stint was short-lived; before his second season, the coaching staff moved him back to right guard, where he became one of the most formidable interior blockers of his time.

Gray epitomized the classic open-field pulling guard with a perfect blueprint. He had explosive short-area quickness from his stance, enabling him to lead-block on the perimeter with devastating impact. With a fierce, punishing attitude, Gray often dominated defensive ends and linebackers in single coverage, creating large running lanes for stars like John David Crow, Johnny Roland, and Prentice Gautt. His legendary toughness made him a teammate favorite; he was a respected team captain for seven straight seasons and frequently played through serious knee injuries.

While his initial years in Chicago were spent establishing his footing, the franchise's relocation to St. Louis in 1960 coincided with Gray's rise to absolute individual stardom. He secured his first career Pro Bowl invitation in 1961, establishing himself as an elite interior presence. By 1963, Gray had evolved into an untouchable force at right guard, kicking off a seven-year stretch of consensus postseason honors.

His peak performance arrived during the 1964 season, when his dominant drive-blocking and pass protection earned him consensus First-Team All-Pro honors alongside his third Pro Bowl selection. Between 1961 and 1968, Gray was voted to six Pro Bowls (1961, 1963, 1964, 1966, 1967, 1968), serving as the undisputed anchor of the Cardinals' offensive line throughout the entire decade. Gray's relentless individual consistency at right guard earned him All-Pro or All-Conference recognition in seven consecutive seasons from 1963 through 1969.

After twelve seasons and 151 games in a Cardinals uniform, knee injuries finally caught up with the veteran leader, leading to his release prior to the 1970 season. He closed out his career with a single season in Houston before hanging up his cleats.

Gray was named as a First-Team guard on the NFL 1960s All-Decade Team, cementing his status as one of the premier interior linemen of his generation.