Born in Algona, Iowa, Seiler played college football at the University of Notre Dame and was a member of the school's 1966 team that won the national championship. In the 1967 NFL Draft, the Jets selected him with the 12th overall pick. Seiler played in two games for the Jets in the 1967 AFL season, but a leg injury led the Jets to put him on a "waived injured list". In 1968, he enlisted in the military and did not play that season. Seiler returned to the Jets in 1969, playing in 11 games. After undergoing offseason leg surgery, the Jets released Seiler before the start of the 1970 season. From 1971 to 1973, Seiler played for the Raiders. He played in 26 games, starting once in 1973, his last NFL season.