Drafted seventh overall by the White Sox in the 1989 MLB draft, Thomas made his major league debut the following year and immediately impressed with his hitting ability. Thomas was named the AL's Most Valuable Player (MVP) by unanimous vote in 1993. That year, he became the first White Sox player to hit 40 home runs and led the team to a division title. He repeated as MVP in the strike-shortened 1994 season, batting .353 and leading the league in slugging percentage and runs. Following two sub-par seasons, Thomas lost a close MVP vote in 2000 despite posting career highs of 43 home runs and 143 RBI. Still, he was named AL Comeback Player of the Year, and Chicago finished with the AL's best record. Later in Thomas's career, a variety of foot injuries and minor ailments reduced his productivity and often limited him to a designated hitter role. In 2005, his final season in Chicago, he was limited to only 34 games after starting the year on the disabled list and then fracturing a bone in his foot close to where it was surgically repaired the previous off-season. He was unable to play in the post-season while the White Sox won the World Series that year. Thomas spent the final three years of his career with the Oakland Athletics and Toronto Blue Jays, with whom he hit his 500th home run.