Previously he has served as transactional and regulatory counsel in the areas of corporate and financial law, capital markets, real estate and infrastructure, and government affairs.  His track record includes participating in the financing of a six-star hotel in Puerto Rico, multiple corporate reorganizations, complex financing transactions and public-private partnerships, and advising various government entities.

In November 2021, Marrero was confirmed by the Legislature as Secretary of the Department of State. In addition, since 2019 Marrero has served as executive director of the Financial Advisory Authority and Fiscal Agency, leading Puerto Rico's debt restructuring efforts, management and oversight of federal funds through the Cares Act and ARPA, and other fiscal and economic efforts.

Previously, Marrero had served as Executive Director of the Puerto Rico Ports Authority from January 2017 to March 2018, in addition, from January 2017 to July 2019, as Executive Director of the Convention District Authority and Executive Director of the Puerto Rico Public-Private Partnerships Authority (PPPA). He also served as Vice Chairman of the Board of Governors of the Electric Power Authority. Moreover, from February 2018 to July 2019, he served as the Governor's Authorized Representative (GAR) to the Federal Emergency Management Agency (FEMA) and Executive Director of the Central Office of Recovery and Construction (COR3), an office attached to the AAPP. In addition, Marrero served as Secretary of the Puerto Rico Department of Consumer Affairs under the administration of former Governor Luis Fortuño. Furthermore, for seven years he worked as an adjunct professor at the Interamerican University of Puerto Rico School of Law where he taught corporate law courses.