In 1981, the Károlyis, along with fellow Hungarian-Romanian team choreographer Géza Pozsár, defected during a gymnastics tour in the United States.

Béla's status as "Nadia's coach" quickly attracted gymnasts to the club, and by the late 1980s, the Károlyi gym had become the preeminent training facility in the United States.

Márta Károlyi has avoided most of the controversy and accusations of abusive coaching that have trailed her husband, opting for a quieter, less abrasive approach.

In the Károlyi coaching team, Béla was often known as the "motivator," while Márta was the "technician," applying her gymnastics savvy to help her athletes learn and perfect their technique, mechanics, and form.

His approach was protested and resisted by both the national-team gymnasts and their coaches, who, by the 2000 Olympics, were so frustrated and unhappy that they spoke about the situation publicly.

Among her duties were selecting athletes for competitions, determining apparatus lineups at the meets, and making recommendations about skills and routine compositions.

At the 2012 Olympics, after Aly Raisman was given a score of 14.966 in the balance beam final, which put her a tenth of a point behind Cătălina Ponor of Romania, Károlyi requested a video review.

As a result of the review, Raisman was awarded an additional tenth of a point for difficulty, allowing her to win the bronze medal on a tie breaker.

The Karolyis retreated from the public eye after the USA Gymnastics sex abuse scandal and their whereabouts are unknown, with some speculating that they returned to Romania.