He received his bachelor's degree in business administration with a major in management and education from the University of Puerto Rico.
After graduating, Marrero worked as a teacher for the Puerto Rico Department of Education from 1970 to 1972.
In 1974, he started working as deputy director of the Ecotactics Program for the Municipality of San Juan.
He presided over the Assembly until 1984 when he resigned to take over the Senate seat left by Guillermo Campos Ayala in the District of Bayamón.
[1] That term he was chosen by his fellow senators as President pro tempore, under Charlie Rodríguez.