From 1979 to 1999, Estus served as principal environmental advisor to four Florida governors. He represented governors and the State of Florida before the State Legislature and Congress, and oversaw the policy and budgets for the State’s Departments of Environmental Regulation, Transportation, Community Affairs, and its five water management districts.

During this tenure, Estus was involved in all major Florida environmental and conservation programs and issues. Early in his career, he helped establish the state’s environmental impact statement review process; He administered this program from 1971 to 1999. He also administered the Florida Outer Continental Shelf Oil and Gas Program from its inception; and oversaw state approvals of federal and federally funded projects in Florida.

With Governor Bob Graham, Estus co-created Florida's Save Our Everglades program in 1983, which evolved into the Comprehensive Everglased Restoration Program (CERP). He was principal staff person in the development and implementation of Florida's notable environmental land acquisition programs – Conservation and Land Acquisition (CARL), Save Our Rivers, Save Our Coasts, and Preservation 2000.

On his retirement, President Bill Clinton wrote to Estus, "You can reflect with pride on a life and career dedicated to the protection of Florida's precious natural resources and to strengthening our nation's environmental policies. I am especially grateful for your efforts to preserve and restore the Everglades."

In 2011 he co-created, with former Florida Governor and US Senator Bob Graham, the Florida Conservation Coalition, consisting of all major Florida conservation organizations, over 40 affiliate organizations and over 2,000 individuals dedicated to protecting Florida's water and natural resources.

Estus was Coordinator of Florida's role and position on the Corps of Engineers Central and Southern Florida Project Comprehensive Review Study.

He spent 25 years active and reserve duty in the U.S. Navy.