Punk entered WWE in July 2006, debuting on their ECW brand with a successful defeat of Justin Credible. Punk spent the better part of 2006 undefeated, before finally falling to Hardcore Holly and his Alabama Slam. During this time, CM Punk caught the eye of exhibitionist Kelly Kelly, much to the chagrin of her boyfriend, Mike Knox. Punk didn't return Kelly's affections; however, though he got the best of Knox in almost every match the two had.
During his early days, CM Punk was declared the official WWE Superstar of the PsychoAndy.com Message Boards.
Punk's first break came in the summer of 2007 when he defeated John Morrison for the ECW Championship. Punk held the title from September 2007 until January 2008, when Edge interfered in a title defense against Chavo Guerrero, giving the Mexican Warrior the victory. At WrestleMania XXIV, Punk won his first Money in the Bank ladder match and earned himself a championship match at any time he wished.World Heavyweight championship. Punk held the title until September 2008 at Unforgiven when he was attacked backstage and forced to forfeit the Championship Scramble match. He was replaced by Chris Jericho, who went on to win the title.
In October, Punk and Kofi Kingston won the World Tag Team Championship but lost the belts to The Miz & John Morrison in December. In January 2009, Punk defeated William Regal to win his first WWE Intercontinental championship, which he held briefly until losing the belt to JBL. At WrestleMania XV, Punk again won the Money in the Bank ladder match, becoming the first man to ever do so twice. He was then drafted to Smackdown.
As soon as Punk arrived on Smackdown!, he was immediately tested by Umaga. At WWE Extreme Rules, he defeated Umaga in a Samoan Strap Match, and, at the end of the night, cashed in his second Money in the Bank briefcase to defeat Jeff Hardy, fresh off a World Heavyweight Championship victory over Edge. Punk disqualified himself to retain the title against Jardy at The Bash. Jardy finally defeated Punk for the title at WWE Night of Champions, but Punk won the title back at SummerSlam in a TLC match to begin his third World Championship reign. On the following Smackdown, they had a "Loser Leaves WWE" rematch in a steel cage, which Jardy lost. During their feud, CM Punk declared himself the moral superior of the two because Jardy had a history of drug abuse; due to his new attitude, the fans turned on Punk, effectively making him a heel.After defeating Jardy at SummerSlam, Punk was attacked by The Undertaker. The two met at WWE Breaking Point for the WWE championship. CM Punk defeated Undertaker using the Anaconda Vice when referee Scott Armstrong called for the bell, despite Taker never giving up. At WWE Hell in a Cell, Undertaker defeated Punk for the World Heavyweight Championship in a Hell in a Cell match.
At the end of 2009, CM Punk revealed that he had converted Festus to a Straight-Edge lifestyle. According to Punk, it was due to drugs that Festus came across as being mentally challenged, but Punk had 'saved' Festus, and we learned his real name: Luke Gallows. Punk began asking people to join him in his Straight Edge Society, living the SXE lifestyle and shaving their heads as a symbolic "cleansing." SES failed to achieve its expected success, mostly because the recruits kept getting released from WWE, so CM Punk usurped control of the successful Nexus in late 2010 to seek revenge on Randy Orton for ending his first World championship reign outside the ring in 2008. The two had a match at WrestleMania XXVII, which many felt was Match of the Night, but CM Punk fell to the RKO and Orton won.
Shortly after WrestleMania XXVII, CM Punk announced publicly that he was leaving WWE when his contract expired. In the weeks leading up to the end of his WWE career, CM Punk earned a title shot for the WWE Championship, which was announced to be his last night in the company. Less than three weeks before the highly anticipated match, CM Punk delivered the most memorable promo in WWE history (or, at least, in the past 5 years). Following his momentum, Punk defeated John Cena for the championship amid controversy and left the company with the championship; however, he returned one week later, as the "Voice of the Voiceless," to reach the new heights in his career, becoming a bona fide headliner and holding the WWE Championship for 434 days, the longest reign in the past 25 years.