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Araujo, who is from Lompoc, Calif., previously represented the U.S. at age-group levels through the Under-23 team.
In March, he played for the U.S. U23 team against Mexico in a Tokyo Olympics qualification game.
Mexico won 1-0 and eventually advanced to Tokyo, getting a bronze medal.
As a dual national with Mexican family ties, Araujo was eligible within FIFA's rules to switch national teams and was yet to play a competitive game for the U.S. senior team.
"My heart is with Mexico," Araujo said in a statement on Tuesday. "I'm grateful for every opportunity that U.S. Soccer has provided me to help me grow as a soccer player and now I am excited to continue my international career with Mexico."
Mexico faces the U.S. in their 2022 World Cup quaIification group on Nov. 12 in Cincinnati.