WASHINGTON — Leon G. Billings, a former aide to Maine Senator Edmund Muskie and a key author of the Clean Air Act and other landmark environmental laws, has died.

Mr. Billings, 78, died Tuesday in Nashville after suffering a stroke while visiting family.

Born in Montana, Mr. Billings moved to Washington in 1962 and had a 50-year career in politics and public policy. As the first staff director of the Senate Environment subcommittee, Mr. Billings was a primary author of the 1970 Clean Air Act, one of the first and most influential environmental laws in US history and a foundation for current air pollution laws.

Mr. Billings also played a key role in the 1972 Clean Water Act, the primary federal law governing water pollution, and 1977 amendments to both the air and water pollution laws.

Mr. Billings served as Muskie’s environment adviser for more than a decade and later was the Democrat’s chief of staff in the Senate and when Muskie was secretary of state under President Jimmy Carter.

Mr. Billings also taught politics at the University of Southern California and served in the Maryland Legislature from 1991 to 2003, focusing on environmental issues.

He later ran a consulting firm and taught college courses on the Clean Air Act and other laws.

Former Environmental Protection Agency administrator William K. Reilly, who worked in the Nixon White House when the clean air and water laws were signed, called Mr. Billings ‘‘an architect of the new order’’ who did ‘‘great work that the public health has benefited enormously from.’’

Tom Jorling, who was Republican staff director on the Senate subcommittee while Mr. Billings led the Democratic majority, said Mr. Billings ‘‘had tremendous skills legislatively and politically. He was respected and trusted by all members of the committee, majority and minority. His talent and skills led to the enactment of the foundational environmental laws of that era.’’

Despite their partisan differences, Jorling and Mr. Billings became close friends and co-taught courses on environmental law at a number of colleges and universities, most recently Arizona State.

Mr. Billings’s son, Paul, said his father learned the importance of advocating for social justice from his parents.

‘‘There was no greater public health champion. Our air and water are cleaner and Americans are healthier because of Leon Billings,’’ said Paul Billings, senior vice president of the American Lung Association.

Mr. Billings leaves his wife, Cherry Billings, of Bethany Beach, Del., and three children. His first wife, former Maryland Delegate Patricia Billings, died in 1990. Leon Billings was appointed to her seat before winning election in his own right.

Jorling said Mr. Billings was disappointed to see clean air and water laws come under attack from Donald Trump and congressional Republicans, but said the laws have survived previous attacks from the White House and Congress. Trump has called climate change a hoax and vows to cut back the role of the Environmental Protection Agency, which he describes as a job killer.

‘‘Leon’s work helped prevent any wholesale efforts at eliminating or rolling back those statutes’’ in previous administrations, Jorling said. The current fight ‘‘would have been a new challenge for Leon.’’