Sepulveda was born in Austin, Texas. He attended Highland Park High School in metropolitan Dallas, Texas. Sepulveda was a fifth-string punter at Highland Park behind Mark Marynick, Jason Wood, Bud "the wee Scot" Robertson, and Ryan Wolcott. He never made it into a game as a punter.
Sepulveda attended Baylor University, where he played for the Baylor Bears football team from 2002 to 2006. He was a walk-on to the football team as a linebacker, and after a redshirt freshman season (despite not having punted since junior high) became the Bears' starting punter, earning a scholarship after the 2003 season. He won the Ray Guy Award tapping him as the best college punter in 2004 and 2006, and was recognized as a consensus first-team All-American in 2004 and a unanimous first-team All-American in 2006. He and Ryan Allen are the only players to win the Ray Guy Award twice.
Sepulveda was drafted in the fourth round (112th pick) by the Steelers in the 2007 NFL Draft. After the release of former starterChris Gardocki, Sepulveda successfully bested Mike Barr for the starting job. Sepulveda signed a three-year contract for $1.46 million with the Steelers on May 31, 2007.
In the first quarter of a December 20 game against the St. Louis Rams, in his rookie season, Sepulveda completed a 32-yard pass to running back Najeh Davenport on a fake punt play.
On July 29, 2008, Sepulveda tore the ACL in his right leg for the second time. He had surgery to repair a torn anterior cruciate ligament on August 6. He was placed on injured reserve by the Steelers after the surgery, officially ending his season.
On December 5, 2010, he again injured his right knee in a game against the Baltimore Ravens.Jeremy Kapinos was signed to replace Sepulveda. On July 31, 2011, the Steelers re-signed Sepulveda to a 1-year deal.
In the second quarter of an October 9, 2011 game against the Tennessee Titans Sepulveda completed his second career pass for a first down, a 33-yard pass to Ryan Mundy on a fake punt play.
It was announced on April 4, 2012 that Sepulveda would not return to the Steelers for the 2012 season.