Born in Milwaukie, Oregon, Sonnen grew up in West Linn, Oregon and began wrestling from a young age. He attended West Linn High School, where he was a state runner-up. In 1996, Sonnen began training in boxing, with the hope of competing in the UFC upon graduating from high school.

After high school, Sonnen attended Brigham Young University before transferring to the University of Oregonwhen BYU began considering cutting their wrestling program. At Oregon, Sonnen earned All-American honors, was a two-time PAC-10 runner-up, was a silver medalist at the 2000 Greco-Roman World University Championships, and was a two-time Dave Schultz Memorial Institutional Greco-Roman winner. He graduated from the University of Oregon with a Bachelor of Science degree in sociology.

Sonnen started his mixed martial arts career in 1997 at the age of 19, by defeating Ben Hailey in Vancouver, Washington. He next defeated future ICON Sport Middleweight Champion andStrikeforce Middleweight contenderJason "Mayhem" Miller. He won his first six fights, before losing to Trevor Prangley. In late 2003, he was submitted by future Ultimate Fighterwinner and UFC Light Heavyweight Champion Forrest Griffin with a triangle choke submission.

 Over years, Sonnen fought some of the best fighters in the world at middleweight and light heavyweight, but often came up short against top ten-level opponents. That all changed in 2008, when Sonnen became the first man to defeat Brazilian WEC Middlweight Champion Paulo Filho. The match itself was infamous as Filho came in to heavy, and it became a non title contest. Filho, who had a previous submission victory over Sonnen, seemed crazed in the fight and seemed not to want to fight. He later mailed the belt to Sonnen, as he felt Chael deserved the title, even the the WEC was disbanding its middleweight division. 

Although he is not known for his finishing ability—more than half of his career wins have come by way of decision—Sonnen is himself notoriously difficult to finish, and his size, physical strength, tenacity and wrestling skill make him one of the most difficult men to deal with in the middleweight division. Always known for being brash, Sonnen's recent UFC success has only increased his level of chatter.

After the victory, a seemingly reinvigorated Sonnen moved to the UFC’s middleweight division and defeated Dan Miller, Yushin Okami, and Nate Marquardt, all of them by dominant Unanimous Decision, to become the top contender to Anderson Silva’s middleweight belt in 2010. In their first match, Sonnen dominated Silva for four rounds, who had previously looked invincible during his title reign. However, Silva was able to catch Sonnen in a triangle choke late in the final round to retain the championship. After the fight, it was speculated that there would be an immediate rematch. However, Sonnen tested above the limit of the approvable ratio of testosterone, and was suspended. It was revealed Sonnen had begun Testosterone Replacement Therapy or TRT. He would later be allowed to fight with the medication, but only as long as he kept his levels in check. 

Following his suspension he would pick up a submission victory over Brian Stann and a close decision over Michael Bisping to earn a rematch with Anderson Silva. After winning the first round in a manner similar to their first fight, Sonnen was stuffed on a takedown in the second round. He then slipped during an attempt to land a spinning back fist, and was hit by a debatable knee, before being finished by the "Spider." Following his second loss at the hands of Silva, Sonnen would look to chase another UFC championship as he moved back to light heavyweight in 2013 to face Jon Jones.

Sonnen would sign on to coach opposite of Jon Jones in the next Ultimate Fighter series with the two of them scheduled to face off on April 27th at UFC 159. His team would win the finale earning Sonnen a Harley Davidson a motorcycle. However the fight against Jones wouldn't turn out in his favor. Chael was finished in the first round with some ground and pound from the champ. After the fight Chael hinted that this could have been his last fight but he had to think it over. He thought it over and would return to the octagon at light heavyweight when he faced off against Mauricio "Shogun" Rua at the launch of Fox Sports 1 for Fight Night 26. Sonnen would walk away with a submission win when he caught Shogun in a guillotine in the first round. The win would also earn him Submission of the Night. He would lose his next fight by tko at the hands of Rashad Evans at UFC 167.

Sonnen would coach the Ultimate Fighter for a second time, this time opposite Wanderlei Silva for The Ultimate Fighter Brazil 3. The two have had heated confrontations already and should make for an entertaining bout when finally meet up (after 2 cancelled bouts) at UFC 175: Weidman vs. Machida on July 5th, 2014.

Following a failed drug test in June, 2014, Sonnen was removed from his UFC 175 bout against Vitor Belfort. He summarily announced his retirement from MMA on June 11. 

After retiring from active MMA competition Chael has remained active within the martial arts media beginning a podcast and competing in pro grappling including grappling to draw against former opponent Renato 'Babalu' Sobral at 'Metamoris VI' and submission loss to Andre Galvao at 'Metamoris IV'.

On November 11, 2014, ESPNannounced it had hired Sonnen as an MMA analyst. He debuted on November 14, previewing UFC 180.

On May 6, 2015, professional wrestlingpromotion Global Force Wrestling (GFW) announced Sonnen as an "expert analyst" for its future events.On July 24, Sonnen was revealed as part of the announce team for GFW's Ampedprogram.

On September 2, 2015, it was announced that Sonnen signed with theWorld Series of Fighting to become a member of their broadcast team beginning at WSOF 23.