Tomczak played football at Thornton Fractional North High School in Calumet City where he was coached by his father Ron Tomczak. After earning Illinois High School Player of the Year honors, he won an athletic scholarship to The Ohio State University. While at OSU, he helped lead the Buckeyes to two Big Ten championship seasons. He graduated from OSU with a major in Communication.
Tomczak went undrafted out of college and signed as an original free agent with the Chicago Bears. He started no games his first year but did earn a Super Bowl ring, and saw playing time in Super Bowl XX on January 26, 1986, during the fourth quarter of the Bears' 46-10 win over the New England Patriots.
He played for the Bears until 1990 starting 31 games and throwing for 31 touchdowns and 47 interceptions. After spending a year at Green Bay and another at Cleveland, he signed with the Pittsburgh Steelers and spent seven seasons with the team, starting for much of the 1996 season and helping to guide the team into the playoffs. He also started occasionally throughout his last three seasons with the Steelers, spelling the inconsistent Kordell Stewart for long stretches of the year in 1999.
After his contract with Pittsburgh was not renewed, he signed with the Detroit Lions in 2000 but suffered a broken right tibia in an exhibition game against the Oakland Raiders. After being forced to sit out the entire season, he retired from football, the last remaining active player from the '85 Bears team.
For his career, Tomczak has 73 starts, completed 55.3% of his passes for 88 touchdowns and 106 interceptions.
Tomczak worked as a sports announcer in Pittsburgh, as well as a color announcer for ESPN college football games, before becoming a sports management agent. He is currently a director at SMG Sports Management and has continued to work as a sports commentator.