Nicknamed "The Punisher", and standing at a height of 6 feet 2 inches, Williams was unusually tall for the three divisions in which he competed.

In 2005 he outpointed former Olympic bronze medalist Terrence Cauthen and, later that year, he knocked out Alfonso Sanchez in 5 rounds.

Williams made his HBO debut against then-undefeated Walter Matthysse, winning by a tenth-round technical knockout.

The match took place July 14, 2007, in Carson, California, at the Home Depot Center with Williams winning a unanimous decision in which turned out to be a close fight where Williams' seemingly stronger finish seemed to seal him the decision victory in the eyes of boxing experts and fans alike.

Williams was then preparing to fight Middleweight Champion Kelly Pavlik in a bout scheduled to take place on October 3, 2009, in Atlantic City, New Jersey.

In the first round Martinez was knocked down due to bad balance and a grazing left hand that landed just below the ear.

After his close win over Sergio Martínez, Paul Williams moved on to face Puerto Rican prospect Kermit Cintrón.

In the fourth round, Kermit Cintron fell out of the ring unintentionally and was not allowed to continue fighting due to hitting the arena floor.

Williams was ahead on two of the three judges' scorecards at the time of the stoppage and was declared the winner by split technical decision.

[10] A highly anticipated rematch with Sergio Martinez eventually materialized at Boardwalk Hall, Atlantic City, New Jersey on November 20, 2010.

On July 9, 2011, Paul Williams fought in a light middleweight contest in Atlantic City against former Cuban amateur sensation Erislandy Lara.

[17] "I'm just chilling in a wheelchair because I got tired of walking," Williams said in an interview with Jim Gray on Showtime Championship Boxing on the day he was supposed to fight.