Hayes has led White House work on clean energy deployment issues (including offshore wind, onshore renewable energy, and transmission siting and permitting), climate resilience (including establishing new interagency structures, funding, data and mapping tools to address cross-cutting resilience issues) and greenhouse gas emission reduction and carbon sequestration initiatives.

Before and between his service in the Clinton and Obama administrations, Hayes practiced environmental and energy law as Global Chairman of the Environment, Land and Resources department at the firm of Latham & Watkins (1990–1997; 2001–2008).

During Hayes' first tenure as Deputy Secretary of the Interior, he focused on environmental priorities, including the acquisition and protection of threatened lands (e.g., the Headwaters old-growth redwood forest in Northern California); the restoration of threatened ecosystems (e.g. the Bay-Delta ecosystem restoration project in California); the introduction of modern water management approaches in the west (e.g. the Colorado River initiatives undertaken by the Clinton administration); the negotiation of habitat conservation plans under the Endangered Species Act; energy-related issues associated with federal lands and resources (e.g. oil and gas development, hydropower licensing, etc.

[3] Hayes’ confirmation was delayed, and subject to a cloture vote, based on then-Senator Bob Bennett’s objections to Secretary Salazar's cancellation of an oil and gas lease sale in Utah.

[6] He oversaw the establishment of a network of climate science and regional cooperatives to address climate change impacts on resources; managed the day-to-day response to the Gulf Oil spill; negotiated a resolution of the Cobell Indian trust fund litigation and oversaw the settlement of several Indian water rights settlements; and was the point person for the Administration on water issues in California and energy issues in Alaska.

[13] During the 2007–2008 academic year, Hayes was a consulting professor at Stanford University's Woods Institute for the Environment,[14] where he undertook a special project analyzing the regulatory challenges associated with carbon offsets.