Marin was a pitcher in college. He remained at the University of Arkansas-Little Rock as an assistant coach in 2005. In 2006-2007, he was pitching coach of Los Angeles Valley College. He then was pitching coach for Harvard-Westlake High School in 2008-2009 (when Lucas Giolito was there). He became pitching coach for the AZL Rangers midway into their 2010 season. In 2015, he captured South Atlantic League Coach of the Year honors with the Hickory Crawdads, when he led a talented Crawdads pitching staff to the 2nd-lowest ERA (3.19) in the South Atlantic League.

He left the Rangers organization in 2017 to spent two seasons as the minor league pitching coordinator of the Seattle Mariners. In 2019, he rejoined the Rangers as bullpen coach for newly-appointed manager Chris Woodward, but only a year later was appointed pitching coach of the Pittsburgh Pirates in 2020.

• 2010-2012 Pitching coach AZL Rangers
• 2012/2013 Pitching coach Leones de Ponce of the Roberto Clemente Professional Baseball League
• 2013 Pitching coach Spokane Indians
• 2014-2015 Pitching coach Hickory Crawdads
• 2016 Pitching coach High Desert Mavericks
• 2016 Pitching coach Surprise Saguaros of the Arizona Fall League
• 2017-2018 Minor league pitching coordinator Seattle Mariners
• 2019 Bullpen coach Texas Rangers
• 2020-2025 Pitching coach Pittsburgh Pirates
• 2026 Bullpen coach Cincinnati Reds

In 2024, Marin helped Paul Skenes win the National League Rookie of the Year Award. He was let go by the Pirates after the 2025 season and was named bullpen coach of the Cincinnati Reds in 2026.

In addition to his coaching in the States, Marin served as a pitching coach for the Leones de Ponce during the 2012/2013 Roberto Clemente Professional Baseball League