Toshi Seeger, who was a driving force and partner in a variety of musical and environmental endeavors with her husband, the folk singer Pete Seeger, died on Tuesday at their home in Beacon, N.Y. She was 91.

His family announced the death.

The music impresario George Wein recalled in an interview on Thursday that he and his wife, Joyce, had joined the Seegers in their log cabin overlooking the Hudson River to plan the first Newport Folk Festival in 1959. He said that Mrs. Seeger suggested performers and helped come up with the idea that no musician, whether a star or an unknown, would be paid more than $50.

“Without Toshi, it couldn’t have happened,” Mr. Wein said.

Mr. Seeger, now 94, became famous for shaping modern folk music through prolific songwriting and peripatetic entertaining, and for his activism. He fought McCarthyism, marched beside the Rev. Dr. Martin Luther King Jr. and led many environmental campaigns.

In an interview on Thursday, Mr. Seeger called his wife of almost 70 years “the brains of the family” and said it was she who figured out how to turn his artistic concepts into commercial successes.