Stasiak made his World Wrestling Federation (WWF) debut on the April 13, 1999 episode of Sunday Night Heat as Meat, attacking Tiger Ali Singh. He soon became the storyline "boy-toy" of the Pretty Mean Sisters (Terri Runnels, Jacqueline, and Ryan Shamrock), although Shamrock left the company a few months later. Meat picked up many victories for a few months over the likes of Droz, Brian Christopher, and The Blue Meanie. However, he would soon be relegated to that of a jobber. This led to Jacqueline leaving Meat and Terri by themselves.
The character only lasted a few months before he split from Terri after Terri saw Meat kissing Marianna, Terri's nemesis, on the Titantron. This led to her and Chaz attacking Meat. In the next couple of weeks, he dropped the Meat name and began to compete under Shawn Stasiak. At Survivor Series, Stasiak was defeated by the debuting Kurt Angle. Stasiak was released in December 1999.
Stasiak made his World Championship Wrestling (WCW) debut on the April 10, 2000 episode of Nitro by attacking Curt Hennig. He later joined the New Blood and began feuding with Hennig. He was soon given nicknames such as "The Perfect One" and later "PerfectShawn" Stasiak, the latter of which was a parody of Hennig's "Mr. Perfect" character. Stasiak picked up two victories over Hennig, one of which was Stasiak's WCW pay-per-view debut on May 7, 2000 at Slamboree. Hennig soon became impressed with Stasiak and briefly coached him before Hennig's WCW contract expired in June 2000.
In late-May, Stasiak formed the tag team called the Perfect Event with Chuck Palumbo, and they soon won the World Tag Team Championship after defeating KroniK (Brian Adams and Bryan Clark). After winning the titles, they began feuding with KroniK over them. In August, the Perfect Event helped form The Natural Born Thrillers alongside Mike Sanders, Sean O'Haire, Mark Jindrak, Johnny the Bull, and Reno, while they were briefly "coached" by Kevin Nash.
Stasiak and Palumbo would later win the World Tag Team Titles two more times before splitting in early January 2001, when Stasiak and Palumbo won a tag team battle royal with O'Haire and Jindrak. Sanders declared both teams victorious and that one member from each team would start teaming together and get a tag team title shot against The Insiders (Diamond Dallas Page and Kevin Nash). Palumbo began teaming with O'Haire and they defeated the Insiders and became the World Tag Team Champions, while Stasiak and Jindrak began teaming together. In February 2001, the Natural Born Thrillers broke up when Stasiak and Jindrak became jealous of Palumbo and O'Haire. The two teams faced off at SuperBrawl Revenge on February 18, 2001 for the World Tag Team Titles, but Palumbo and O'Haire retained.
In March 2001, Stasiak acquired the services of Miss Hancock as his valet, gaining the nickname "The Mecca of Manhood" in the process. He was also, in storyline, hinted as the alleged father of Hancock's baby, which later turned out to be a stack of 8x10 cameras in a stroller. As a heel, Stasiak used the cameras to take pictures of himself before throwing the pictures to fans as a way to show off his physique. While with Miss Hancock, he also started a brief feud with Bam Bam Bigelow. The feud culminated on the very last episode of Nitro on March 26, 2001, as Stasiak defeated Bigelow in a tattoo match. Following this, WCW was purchased by the World Wrestling Federation and most of the talent contracts, including Stasiak's, were picked up.
Stasiak returned to the WWF in July 2001 as part of The Alliance after WCW was bought by the WWF. Stasiak won at InVasion, where he, Kanyon, and Hugh Morrus defeated The Big Show, Billy Gunn, and Albert. Throughout August, he was given the gimmick of being clumsy while trying to impress the Alliance's leader, Stone Cold Steve Austin. Every time he tried attacking major WWF stars such as The Rock or Kurt Angle, he would run into a wall, statue, milk truck, or just completely miss and trip over his boots. In late August, Stasiak was also briefly paired with Stacy Keibler again, but she stopped being his valet in late September to manage the Dudley Boyz. He was injured soon after and was out of action until late October.
On November 18 at Survivor Series, Stasiak, in storyline, lost his job along with all of the Alliance members when Team WWF defeated Team Alliance. The Alliance members still worked house shows and dark matches for a while, however, until being ready to be called up to the main active roster. However, Stasiak was injured in late November and required surgery on his knee. He was later cleared to wrestle on January 1, 2002.
Stasiak was returned on the Raw brand in late-March 2002 and had his return televised match on the April 7, 2002 edition of Sunday Night Heat, defeating Tommy Dreamer and on the following week of Sunday Night Heat, Stasiak was defeated by Goldust.
Stasiak made his return on the April 15, 2002 episode of Raw with a new character that saw him claim that he was from Planet Stasiak, heard voices in his head, talked to himself with rhymes, and acted comically insane. On this same night, Stasiak was defeated by Big Show. Stasiak traded the Hardcore Championship several times with the likes of Steven Richards, Justin Credible, Bradshaw, and Tommy Dreamer until he requested his early release on September 27, 2002.