Fletcher died Monday night at age 89. The cause of death was not immediately known, according to court spokesman David Madden.
She was appointed to the bench by President Jimmy Carter in 1979. Fletcher was known for rulings upholding affirmative action, allowing claims of workplace discrimination to proceed, overturning death penalty cases and protecting the environment.
Fletcher was one of the first female partners at a major law firm in the country, and the second woman appointed to the 9th Circuit.
Although her body began to fail her toward the later years, Seattle U.S. District Judge Robert Lasnik said Fletcher kept hearing cases and remained sharp.
In 1996, Republican Utah Sen. Orrin Hatch insisted that because of an obscure, 19th century anti-nepotism law, Fletcher needed to take senior, or semi-retired, status before her son, 9th Circuit Judge William A. Fletcher, could join the court.
Betty Fletcher agreed, but instead of slowing down as a semi-retired judge, she maintained a full caseload.
"Throughout her life people underestimated her," said Seattle U.S. Attorney Jenny Durkan. "The thought that taking senior status would mute her voice or her ideas was a huge miscalculation."
After attending Stanford at 16 years old and graduating from University of Washington's law school in 1956, Fletcher immediately ran into trouble because law firms were not hiring women.
She said she pounded the pavement with her resume until she was hired at the Seattle firm Preson, Thorgrimson and Horowitz. She later served as the first female president of the King County Bar Association.
Fletcher's husband of 69 years, University of Washington law professor Robert Fletcher, died late last year. She is survived by her four children.
The Associated Press contributed to this report.