Marcus Thomas is a 2003 graduate of Tolleson Union High School in Tolleson, Arizona. Marcus spent his sophomore year in high school backing former University of Arizona, Denver Broncos, New Orleans Saints, Philadelphia Eagles and Cleveland Browns running back Mike Bell. During his junior year, he ran for over 2,000 yards while leading Tolleson to the 4A state playoffs. His senior year, he was named Arizona State High School Player of the Year and a Parade All-American after setting Arizona high school records for rushing yards in a season with 3,573 yards rushing and 46 touchdowns. Breaking records set by former teammate Mike Bell. He also set the state record for 400-yard rushing games in a season and career and the single game record of 424 yards against Phoenix Moon Valley High School. Marcus left Tolleson as the state of Arizona's all-time leading high school rusher with 5,878 yards and only the third back in state history with back-to-back 2,000-yard rushing seasons.
Thomas was signed to the practice squad of the Dallas Cowboys on December 17, 2008 and remained there through the end of the season.
Thomas signed with the Denver Broncos on August 12, 2009. He was waived on September 4.
