When second-string tight end Jerame Tuman was placed on injured reserve, Spaeth was promoted to second-string. Spaeth caught 5 passes for 34 yards and 3 touchdowns in the 2007 NFL season. In the 2008 season, Spaeth added 17 more catches to his career and 136 yards during the regular season. Along with both an increase in catches and yards, Spaeth also played in Super Bowl XLIII where he had one catch for six yards. The Steelers went on to win 27-23 over the Arizona Cardinals. In 2009, Spaeth had 5 catches for 25 yards and 1 touchdown. At the end of the 2010 season, Spaeth and the Steelers appeared in Super Bowl XLV against the Green Bay Packers. He had one reception for nine yards in the 31–25 loss. As an unrestricted free agent following the 2010 season, Spaeth signed with the Chicago Bears, who then traded away tight end Greg Olsen. Spaeth scored his first touchdown catch with the Bears in Week 1 against the Atlanta Falcons on a one-yard pass from Jay Cutler. On March 13, 2013, Spaeth was released by the Bears, being the last Bear to wear number 89, which was retired on December 8, 2013, in honor of tight end and Super Bowl XX winning head coach Mike Ditka. On March 15, 2013, Spaeth re-signed with the Pittsburgh Steelers. On November 2, 2014, he caught Ben Roethlisberger's record-breaking 12th touchdown in two games. On March 9, 2015 it was announced that the Steelers had signed Spaeth to a two-year contract extension. On July 21, 2016, the Steelers released Spaeth due to a failed physical.