In October, at age 14, Douglas moved into the home of Missy Parton in West Des Moines, Iowa, to train under Liang Chow, the former coach of 2007 World Champion and 2008 Summer Olympics gold medalist Shawn Johnson. Although Douglas' former coach, Walker, stated in 2012 that she was convinced Douglas could have made it to the Olympics if she had remained in Virginia Beach, Douglas said, "Something clicked in my head that said, if I really want to make this happen I need to get better coaching." The impetus for Douglas' move to Iowa was when Walker had invited Chow to teach a clinic at her gym, Excalibur. Douglas was impressed when Chow was able to teach her how to perform the Amanar vault in a single afternoon. Douglas considered a move to Texas to train with a renowned coach there, but after that coach declined to train her out of loyalty to Walker, Douglas selected Chow. Chow was initially skeptical, since Douglas had been just one of hundreds of children at the clinic in Virginia Beach. However, Chow subsequently informed Douglas's Excalibur coaches that he had agreed to train her, but pointed out that he did not recruit her, saying, "I would never recruit anybody to my program." Later on, Douglas suffered from a hamstring strain and a hip flexor injury in July. She couldn't do much during this time, but this allowed her to improve her bar skills.
At the 2012 Olympic Trials held in San Jose, California on July 1, Douglas placed first in the all-around rankings, securing the only guaranteed spot on the women's Olympic gymnastic team.
At the 2012 Summer Olympics gymnastics event at the O2 Arena (North Greenwich Arena) in London, Douglas and her teammates – Jordyn Wieber, McKayla Maroney, captain Aly Raisman and Kyla Ross (collectively nicknamed the "Fierce Five"), won the team event gold medal at the 2012 Summer Olympics – the first since the "Magnificent Seven", including Shannon Miller, Dominique Moceanu, Kerri Strug and Dominique Dawes, did so as hosts in Atlanta in 1996. Douglas was the only gymnast on the team to compete on all four apparatus (vault, uneven bars, balance beam, and floor exercise) during the finals of the team competition. She then won the gold medal in the individual all-around, becoming the first African-American woman, as well as the first woman of color of any nationality, to win the event. She also became the fourth American woman to win Olympic all-around gold as well as the third straight to do so (after Mary Lou Retton in Los Angeles in 1984, Carly Patterson in Athens in 2004 and Nastia Liukin in Beijing in 2008, all of whom were at the venue and watched Douglas equal their feat.) She also became the first American gymnast ever to win both the team and individual all-around gold at the same Olympics.
In December 2012, the Associated Press named Douglas the Female Athlete of the Year. She became the fourth gymnast to receive the honor.
In July 2012, Douglas and her teammates were featured on the cover of Sports Illustrated Olympic Preview issue, the first time an entire Olympic gymnastics team had been featured on the cover of the magazine. On July 20, Douglas was on one of five Time magazine Olympic covers.
In September 2012, Nintendo announced that Douglas would be part of a new ad campaign for New Super Mario Bros. 2. On September 4, Douglas led the Pledge of Allegiance at the 2012 Democratic National Convention in Charlotte, North Carolina.
In December 2012, Douglas released her autobiography, Grace, Gold, and Glory: My Leap of Faith. The book debuted at number four on The New York Times Young Adult Bestseller List. That same month, she performed a miniature floor routine at the 2012 MTV Video Music Awards as part of the live performance by Alicia Keys and Nicki Minaj of the Girl on Fire Inferno Remix – following Douglas' success in London, Minaj had opted to end her verse with a reference to her: "I ain't tryna be that / Haters wanna see that / But I got 'em aggy / 'Cause I win the gold like Gabby."
