He signed for Chivas USA in March 2009, just before the new season.[3] Trujillo started 18 games and made three substitution appearances for Chivas USA in his first season. He became a regular starter for the team in his second year, and inherited Jonathan Bornstein's role as captain when Bornstein was not active.
Trujillo remained with Chivas USA through the 2011 season. At season's end, the club declined his 2012 contract option and he entered the 2011 MLS Re-Entry Draft. Trujillo was not selected in the draft and became a free agent.
Mariano is now a member of Jaguares de Chiapas, Mexican soccer club. No longer an active player, Jose Guadalupe (Jaguares Head Coach) has integrated Mariano to his Coaching Staff upon the 2012 Liga MX season to start July, 20th. Jaguares's coach Jose Guadalupe Cruz saw him play during a training session with the other players so he convinced Mariano Trujillo to be a team player for the Copa Mexico where he gave an assist to Antonio Salazar in a 1–0 win at home against Necaxa on July 24, 2012.
International
Trujillo played two games with the Mexico national team in 2003, his first against El Salvador in Carson, California. He scored his only international goal in a friendly match against Peru in East Rutherford, New Jersey. Trujillo was also a member of Mexico's U-20 squad at the 1997 World Youth Championship in Malaysia, alongside former Chivas USA forward Eduardo Lillingston.