Prior to his arrival in the World Wrestling Federation, Sean was best known as the Lightning Kid in the GWF where he feuded with Jerry Lynn. Upon his arrival in the WWF he was given a number of names such as the Kamikaze Kid until he managed an "upset" win over Razor Ramon. At this point, he was given the name 123 Kid.
He continued using this name until his departure for WCW in 1996 to join the heel stable known as the NWO. To play upon his previous gimmick of the 123 Kid, he was given the name Syxx because 1+2+3=6. Syxx soon became 6Pac. While he was out injured, he was fired in an effort by then WCW President Eric Bischoff to control Sean's friends Kevin Nash and Scott Hall and to prove to them that he was in charge.
Sean returned to the WWF, where he became known as XPac. He was immediately inducted into the Degeneration X heel group and cut a promo against Bischoff and Hulk Hogan as well as claiming that if contractually free to do so, Hall and Nash would have been joining him in returning to the WWF. This was one of the seminal events that lead to the WWF permanently regaining the status of number one wrestling promotion from WCW. Up to this point in the Monday night wars, wrestlers only jumped from the WWF to the big money, guaranteed deals available in WCW. Sean's return proved that it was a two way street. This, combined with Vince Russo's vision of the Attitude Era, Stone Cold Steve Austin's first World Title reign (and the subsequent McMahon vs Austin feud) and Mick Foley's insane, suicidal, stuntman bumps in his King of the Ring Hell in the Cell match against the Undertaker eventually led to the WWF driving WCW out of business.
Years later when Hall, Nash and Hogan returned to the WWF and Hogan's nostalgic popularity required that he be turfed from the latest incarnation of the NWO, XPac, who had been out with an injury, returned and immediately attacked Hogan, claiming he'd been waiting three years to do so. This angle was immediately dropped.
About the time they brought in Eric Bischoff as GM of WWF Raw, XPac ended up leaving the WWF in a mutual decision. This unfortunately negated any chance of following up on the other half of the promo from three years ago.
Sean joined the NWA:TNA promotion upon leaving the WWF and began using the name Syxx-Pac.
Behind the scenes Sean was a member of the Clique. He briefly led a heel group known as X-Factor, whose members included Albert and Justin Credible.
Sean was engaged to Joanie Laurer, who formerly played the role of Chyna in WWF, but the relationship ended after she accused Waltman of domestic violence.