Tomlin grew up around Lynchburg, Virginia, and attended Liberty University. Selected by the Pirates in the 18th round of the 1988 Major League Baseball (MLB) Draft, he reached the major leagues in 1990. In 1991, he finished eighth in the National League (NL) in ERA (2.98) and held the Atlanta Braves to two runs over six innings in Game 4 of the NL Championship Series, earning a no decision in a 3–2 victory. The next year, he was tied for the NL lead in wins through June 22 and finished the year with the 10th-best winning percentage in the NL. Injuries limited him to 18 starts in 1993, and he had elbow surgery after the season. He only appeared in 10 games for Pittsburgh in 1994 and did not pitch at all in 1995. After two seasons in minor/independent league baseball, he became the pitching coach for Liberty University. After serving in that capacity through 2006, he served as a minor league pitching coach for the Washington Nationals for a few seasons.