[7] Shields is the only boxer in history, female or male, to hold all four major world titles in boxing—WBA, WBC, IBF and WBO, in three weight classes.

[9] Shields was the youngest boxer at the February 2012 U.S. Olympic Trials, winning the event in the 165 lb (75 kg) middleweight division.

[11][18][20] At that time she began boxing at Berston Field House in Flint, where she met her coach and trainer, Jason Crutchfield.

[23][11] In April 2012, she won her weight class at the Women's Elite Continental Championships in Cornwall, Ontario against three-time defending world champion Mary Spencer of Canada; she held an undefeated record of 25 wins and 0 losses at that point.

[28] At the 2012 Summer Olympics in London, aged 17, she won the gold medal in the women's middleweight division after beating veteran Russian boxer Nadezda Torlopova 19–12.

[30] In October 2012, she competed in her second National PAL Championships, beating Franchón Crews-Dezurn in the finals to win gold at middleweight in the open division.

[31] At the 2013 IBA Youth World Boxing Championships in Bulgaria, Shields defeated polish boxer Elżbieta Wójcik to win gold in the middleweight class.

[34] In September, she defeated Canada's Ariane Fortin in the final round to win the middleweight title at the Elite Women's Continental Championships for the second time of her amateur boxing career.

[37] As a result of her performance in the 2015 Pan American Games, she was given the honour of serving as Team USA's flag bearer at the closing ceremony.

[39] Shields won the gold medal at the 2016 AMBC Olympic Qualifying Tournament in Argentina defeating Dominican Republic's Yenebier Guillén in her final bout on her 21st birthday.

[41] Later that year, at the 2016 Summer Olympics in Rio, she won the gold medal in the women's middleweight division by again defeating Nouchka Fontijn of the Netherlands.

[56][57][58] On June 22, 2018, in just her sixth professional fight, Shields defeated Hanna Gabriel by unanimous decision, winning the vacant WBA and inaugural IBF middleweight belts, breaking the record for becoming a two-weight world champion in the fewest professional fights, a record previously held by Vasyl Lomachenko.

Shields was scheduled to fight Ivana Habazin for the vacant WBO junior middleweight title in Flint, Michigan, on October 5, 2019.

[66] The Atlantic boardwalk hall had a sold out Venue as Claressa won by unanimous decision, 99–89, 100–90 and 100–89, and became the fastest ever to win titles in 3 divisions male or female in history.

[67] On March 5, 2021, Shields defeated Marie-Eve Dicaire by unanimous decision to retain her WBC and WBO super welterweight titles, claim IBF 154-pound belt, and vacant WBA light middleweight strap.

[74] Shields was initially scheduled to face reigning WBO Middleweight Champion Savannah Marshall in a title unification bout on September 10, 2022.

[80] On June 3, 2023, Shields defeated Maricela Cornejo by unanimous decision at Little Caesars Arena in Detroit, Michigan to retain her undisputed middleweight title.

[81] Shields was scheduled to challenge Vanessa Lepage-Joanisse for her WBC heavyweight title at Little Caesars Arena in Detroit, MI on July 27, 2024.

[84] On February 2, 2025, Shields faced Danielle Perkins for the undisputed heavyweight championship at Dort Financial Center in Flint, Michigan.

[85] She scored the fight's lone knockdown in the waning seconds of the tenth round and won the bout by unanimous decision with the judges scorecards reading 97-92, 99-90, and 100-89- all for Shields.

[87] In November 2020, Shields had signed a three-year contract with Professional Fighters League and was expected to make her mixed martial arts debut in 2021.

[92] However, on July 12, 2021, news surfaced that her bout was rescheduled to take place on August 19, 2021, in order to garner more exposure at an ESPN-aired PFL 8 event.

[95] In August 2023, it was announced that Shields had re-signed a multi-year contract with Professional Fighters League to continue competing in mixed martial arts.

[111] In December 2016, Shields became the third woman (Cathy Davis, Ronda Rousey) and second female boxer ever to grace the cover of The Ring magazine.