Taylor currently has an undefeated record of 25-0-1, with 17 wins coming by way of knockout. He is married to former Louisiana Tech and WNBA player Erica Smith-Taylor.

Since early in his professional career, Taylor had been touted by many as being the heir apparent to middleweight king Bernard Hopkins. Taylor dominated all of his opponents, scoring wins over respectable fighters such as Raul Marquez and William Joppy. On February 19, 2005, Taylor defeated the previously unbeaten Daniel Edouard via TKO in round 3. With this win, Taylor earned a title bout against Hopkins, who had unified the four major world middleweight titles and was rated by Ring Magazine as the #1 "pound for pound" boxer in the world.

Taylor fought Hopkins for the undisputed middleweight championship July 16, 2005. Taylor outboxed the slow-starting Hopkins early in the fight, winning the early rounds by using his jab and power punches. Although Hopkins gradually became more active and maintained his dominating defense, Taylor continued to fight aggressively and won some of the middle rounds. In the last four rounds, however, Hopkins became the aggressor and battered Taylor, shrinking Taylor's lead on the scorecards. Nonetheless, Taylor survived the late surge and won the fight by close split decision to become the new undisputed middleweight champion.

The split decision was considered to be controversial. One judge, Duane Ford, awarded the twelfth round to Taylor, however if Ford had awarded it to Hopkins, then the fight would have been a draw. Hopkins argued that the decision was extremely controversial however the boxing commission was noncommital on the issue, instead ordering a rematch.

On December 3, 2005, Taylor this time won the rematch against Hopkins by a unanimous decision. Furthermore, Taylor had vacated his IBF title in order to make this fight happen. Overall, far fewer people considered this fight's decision as controversial as the first, even though Hopkins once again won many of the punch statistics. To some fans, this second win proved that Taylor's youth had conquered the aging legend.

On June 17, 2006, Jermain faced off against the number one contender, Winky Wright. In a great, close fight, the judges scored it 115-113, Winky winning one and Jermain the other, and the final judge scoring it a 114-114 draw. The match displayed a contrast of styles; Winky used his peek-a-boo style to force Jermain into the corners where he had advantage. Jermain used his power punches to fight his way out of the corners, in an attempt to keep the fight in the middle of the ring where he was able to outbox Wright. Due to the draw decision, Jermain retained his title.