Walker was selected by the Detroit Lions in the fourth round of the 1958 NFL draft, 45th overall, in December 1957, weeks before Detroit won the NFL title, their third of the decade. He played for the Lions for 15 years from 1958 to 1972. Walker appeared in 200 games for the Lions, a franchise record that was later broken by placekicker Jason Hanson. He also scored 345 points, which ranked third in Lions history at the time of his retirement (currently ninth). As a placekicker, Walker converted 53 of 131 field goal attempts for a 40.5% success rate, the lowest field goal percentage in NFL history. He attempted 13 field goals of 50+ yards in his career, and missed them all. On extra points, he converted 172 of 175 attempts for a 98.3% success rate.