Ruiz was born in Imperial, California; his parents had emigrated from Mexico to the U.S.[2] His father is a former construction worker who started his own business flipping houses.

[5] Ruiz later worked for his father in construction for a time before deciding to become a full-time boxer[2][6] and starting his amateur career in Mexico.

[5] His 105 wins include two Mexican National Junior Olympics gold medals[7] and a title at the Ringside World Championships.

[citation needed] Ruiz also represented Mexico in two 2008 Beijing Olympic Games qualification tournaments, losing to eventual Olympians Robert Alfonso of Cuba and Óscar Rivas of Colombia in the first and second qualifiers.

Ruiz had Freddie Roach in his corner and at the Wild Card Gym and sparred with former UFC heavyweight champion, Andrei Arlovski.

A 19-year-old Ruiz made his professional debut on March 28, 2009, at the Plaza de Toros in Tijuana, Baja California, Mexico, in a four-round bout against Miguel Ramírez.

Ruiz took an eight-month gap before he returned to the ring in February 2010, winning a four-round unanimous decision against Juan Luis Lopez Alcaraz.

A month later, Ruiz made his American debut at the Gaylord Hotel in Texas, knocking out Luke Vaughn in round one.

On February 5, 2011, Ruiz knocked out Kelsey Arnold in the third-round and in the same month defeated Alvaro Morales via unanimous decision 59–55, 59–55, and 60–54.

In July, Ruiz fought at the Texas Station Casino, Las Vegas, defeating Villi Bloomfield via fourth-round TKO.

Willis entered with a record of 1–3–1 in his previous five fights, including a split decision loss three months prior to Denis Bakhtov (33–7).

[20][21] On December 20, 2014, Ruiz fought former WBO heavyweight champion, 38 year old Siarhei Liakhovich (26-6, 16 KOs) at the Celebrity Theater in Phoenix, Arizona.

[25] After a 9-month gap, Ruiz returned to the ring in September 2015 at the Tachi Palace Hotel & Casino in Lemoore, California, defeating Joell Godfrey via unanimous decision over eight rounds, all three judges scored it 80–72.

[27] On May 14, 2016, Ruiz fought 45 year old, former world title challenger Ray Austin (29-6-4, 18 KOs) at the Sportsman's Lodge in California.

[31] Ruiz next fought on September 10, 2016, returning to the Tachi Palace Hotel & Casino in California to headline "Solo Boxeo Tecate" (UniMas) against 40 year old Franklin Lawrence (21-2-2, 16 KOs) for the WBC-NABF heavyweight title.

His only other loss came in his fifth professional fight against future WBC world champion Bermane Stiverne, which was stopped after Lawrence injured his arm in round one.

[37] With his sudden announcement that he would relinquish his heavyweight world title belts due to his various issues, it was unclear exactly how the WBO and WBA would go about filling the vacancies.

But before Fury vacated, Duco Events promoter Dean Lonergan announced in early October he had been negotiating an alternative WBO title fight against Ruiz, suggesting he had a chance of reaching a deal with Bob Arum.

[39] Ruiz failed to become the first heavyweight of Mexican ancestry to win a world title when Parker won the bout by a majority decision.

Ruiz was next to make a ring return on February 3, 2018, on the undercard of Gilberto Ramirez vs. Habib Ahmed WBO super middleweight title fight at the American Bank Center in Corpus Christi, Texas.

[43] Ruiz did not appear on the card and instead his return was pushed back to take place at the StubHub Center in Carson, California on the undercard of Óscar Valdez vs. Scott Quigg on March 10.

[46] His next fight was scheduled to take place on July 7, 2018, at the Save Mart Center in Fresno, California, against veteran journeyman Kevin Johnson (32-9-1, 16 KOs).

Johnson, who had previously only been stopped twice in his nine losses, was known for his toughness, having taken the likes of Kubrat Pulev, Derek Chisora, Tyson Fury and Vitali Klitschko the twelve round distance.

[48] On January 11, 2019, it was reported that Ruiz had signed a deal with powerful advisor Al Haymon, and would now be part of the Premier Boxing Champions (PBC) stable, with his fights being aired on Showtime and FOX.

[49] On March 7, Ruiz's PBC debut was announced to take place on the Danny García vs. Adrián Granados undercard on April 20 at the Dignity Health Sports Park in Carson, California against 36 year old German boxer Alexander Dimitrenko (41-4, 26 KOs) in a ten-round bout.

[57] Prior to the Dimitrenko fight, Ruiz put his name forward to replace Jarrell Miller and challenge Anthony Joshua (22-0, 21 KOs) for the unified WBA (Super), IBF, WBO, and IBO heavyweight titles on June 1, 2019, after Miller was denied a license by the New York Athletic Commission because he failed three different tests for PEDs.

[60][61][62][63] On June 1, Ruiz defeated Joshua by technical knockout in the seventh-round, capturing the unified WBA (Super), IBF, WBO, and IBO titles.

Joshua boxed a disciplined fight, keeping Ruiz at a distance with his jab and using lateral movement to avoid trading punches up close as he had in their first encounter.

[74] Sixteen months after defeating Chris Arreola, Ruiz returned to the ring on September 4, 2022, in Los Angeles to face former WBA interim heavyweight champion Luis Ortiz in an eliminator for the WBC title.

[82][83] Ruiz's right hand appeared to be fractured during the fight with notable visual deformity to the contour of his metacarpal region shown in the post-fight interview.