Councilmember Marcos was selected to fill the unexpired term of former Councilmember Kurt Kroemer in February 2007. He was re-elected in November 2007 and again in 2009 and 2011. He represents District 1 on the City Council.

Marcos is chair of the Bowie Health Center Foundation and served as president of the Greater Bowie Chamber of Commerce from 2004 to 2005. He is the owner of TJ Elliott's Restaurant in Bowie and was one of the founders of the Ledo Pizza chain and the owner of the original Ledo's Restaurant in Hyattsville.

Councilmember Marcos lives in the Northridge section of the city with his wife Terri and his children Miranda and Miles.