Marcus' lobbying career began in the early 1990s when he was a lobbyist for the Arizona Chamber of Commerce where he advocated on behalf of the business community on a broad spectrum of issues. From the Chamber, Marcus was recruited to direct government relations activities at the Arizona Department of Commerce. During his tenure at the Department of Commerce, Marcus successfully lobbied the Greater Arizona Development Authority concerning legislation providing an infrastructure financing mechanism for rural communities. He also represented the Arizona Department of Environmental Quality before the Legislature and Executive branch and helped enact significant legislation in the areas of air quality, waste programs and water quality as well as improvements to the Water Infrastructure Financing Authority.

Since 1998 Marcus has represented a diversity of clients in front of the Legislature and Executive agencies. His areas of experience include insurance, public transit, transportation, economic development, tax policy, environment, infrastructure financing authorities, polling, ambulance certificates of necessity, employment law, public records, campaign management, health care, regulatory reform and education. He has authored public academic book chapters on lobbying, developed strategic government relations plans for multiple organizations, and lectured on strategic planning for government relations.