During his undergraduate studies, Valez interned with Barrett, Hale & Alamo, LLC as a civil engineering intern, where he analyzed hydraulics for PR-10 State Highway Design. After finishing his master's, he served as the Project Specialist Team Leader for the CSA Group, Architects and Engineers in 2012. As a team leader, he guided three junior engineers in developing 100+ infrastructure retrofit assessments for public schools under the second phase of the XXI Century Schools Government Program (Public Schools Renovations Project). Afterward, he joined Barrett, Hale & Alamo, LLC again as an Urban Design Manager, where he served until 2014. In this role, he designed and managed urban transportation projects in San Juan and Cayey municipalities, working with other groups of architects, planners, and engineers.

In 2014, Valez also worked as an Urbanism & Community Development Consultant for Autoridad de Carretera y Transportacion (PR-DOT), where he served under the Executive Director of the Special Communities and Urban Development Office working on projects related to infrastructure in low-income communities. After this consultancy project concluded, he joined Corporacion del Proyecto Enlace del Cano Martin Pena in 2016 as an Urban and infrastructure Program Coordinator. His responsibilities included supporting the implementation of the transportation, stormwater, and waste-water components of a 1-billion-dollar comprehensive development plan focused on community-led visions of ecosystem restoration, equitable development, affordable housing, and climate resilience. This community-led and federally sponsored initiative received the United Nations World Habitat Award in 2016 and, in 2023, the Inaugural Global Impact Award from the American Society of Landscape Architects and the International Federation of Landscape Architects. While in this role, his experience in providing first response and supporting relief efforts in the aftermath of Hurricane Maria convinced him to relocate to the mainland U.S. to engage in climate action directly.

In 2018, Valez started at The Nature Conservancy as an Urban Conservation Project Manager, responsible for implementing the organization's Urban Conservation Program in Philadelphia. In the role, he worked with community stakeholders and technical consultants to support Philadelphia's Green City Clean Waters Plan, arguably the most comprehensive municipal plan to manage urban waters, centering community and social equity to achieve the plan's goal of producing thousands of "greened acres." He worked at TNC until 2020 when he left to become the Senior Program Officer for the Institute for Sustainable Communities (ISC). As Program Officer, he supported community-based organizations and community advocacy entities working to implement equity-driven climate policies across scales. At ISC, he served as the national program office lead for the Kresge Foundation's Climate Change, Health & Equity initiative (CCHE), supporting community-based organizations and health institutions in advancing climate & health equity policy strategies at the local, regional, and national levels.

In 2022, he was awarded a year-long fellowship at Harvard University, becoming a Climate Justice Design Fellow. He participated in a pilot program of Harvard and Google's Data Climate project, which seeks to advance environmental justice, research, service, and education. Valez currently serves on three commissions and boards: PennFuture, Taller Puertorriqueño, and the City of Philadelphia's Environmental Justice Advisory Commission. On the latter, he serves as the Vice-Chair. He works at the World Wildlife Fund as their Climate and Environmental Justice Manager.

In speaking about what keeps him in this field, he highlights the people and communities that fuel him to continue moving forward. The people - your family, friends, community, and people you engage with – are why we are doing this. Working with communities in Philadelphia, Cano Martin Pena in San Juan, and other organizations are among many highlights of his career. Carlos does not see himself becoming disengaged in this work, in part because of his sense of responsibility to others and due to the moments in his career that keep him motivated.