Marjorie Van Cleef, 86, of Wyncote, a music teacher in Philadelphia and Coatesville and a lifelong international peace and social justice activist, died Tuesday, Oct. 26, of breakthrough COVID-19 at Pennsylvania Hospital.

During her long career as a strategist, organizer, and protester for world peace, justice, and equality, Ms. Van Cleef took part, often as a leader, in demonstrations against war, racial bias, police brutality, unfair labor and economic development policies, environmental destruction, and other important issues of her day.

She was especially devoted to ending the use of drones as weapons in war, and she founded the Philadelphia Center City Drone Death Walk/Vigil, and cofounded the Philadelphia Area Anti-Drone Network.

Indefatigable and zealous in pursuit of her goals, she often wrote and spoke publicly about her views, carried banners at the vanguard of marches, and embraced street theater by wearing a death mask and dressing in black at her anti-drone rallies.

“Martin Luther King spoke of militarism as a threat to democracy,” Ms. Van Cleef wrote in a 2016 review of Gregoire Chamayou’s book A Theory of the Drone. “Surely the secrecy in warfare use of drones poses such a threat.”

Ms. Van Cleef addressed police brutality against people of color long before the Black Lives Matter movement surfaced, and she eschewed buying products from corporate giants due to what she considered their exploitation of workers.

In addition to her own groups, she was active with Women Against Military Madness, the Women’s International League for Peace and Freedom, and other organizations. Her large collection of documents associated with those groups can be found at Swarthmore College and other universities.

“She was 100% in when it came to good social activism,” said her friend and colleague Karen Barton, coordinator of the Bryn Mawr Peace Coalition. “She was so sensitive to every issue, even the micro-aggressions she saw every day.”

Ms. Van Cleef was a child musician, playing the piano when she was 4. She earned a bachelor’s degree in music in 1957 at the Conservatory at Oberlin College and a master’s degree in education from the University of Massachusetts in the 1970s.

She was a lifelong church organist, most recently at St. Gabriel’s Episcopal Church in Northeast Philadelphia, and taught music at William H. Shoemaker Junior High School in West Philadelphia and to elementary school students in the Coatesville Area School District and in New Haven, Conn.

She later taught English and writing at community colleges in Pennsylvania, Connecticut, and Illinois. “She loved being a teacher,” said her daughter, Liz.

Born May 3, 1935, in Philadelphia, Ms. Van Cleef grew up in Jenkintown and graduated from Jenkintown High School in 1953. She liked to knit and sew as an adult, and she made her own candles, tended her own organic garden, and bought her books at local shops when she couldn’t get them at the library.

She married Henry Van Cleef and had their daughter and son, Chris. They divorced in 1967, and she met longtime partner Bill Dyson in New Haven in 1979. For more than 30 years, in New Haven and then Bryn Mawr and Wyncote, Ms. Van Cleef and Dyson lived and protested together.

“We liked to laugh and talk about all the things we did,” Dyson said.

In an online tribute, a friend wrote: “Marjorie made a difference. We need to follow her example and to stand up for what we know is right.”

In addition to her children and partner, Ms. Van Cleef is survived by three grandchildren, a brother, and other relatives. Her former husband died in 2019.

A memorial service is scheduled for 11 a.m., Saturday, Nov. 6, at the Memorial Church of the Good Shepherd, 3820 The Oak Rd., Philadelphia. A service in New Haven is to be held later.

Donations in her name may be made to the Native American Rights Fund, 1506 Broadway, Boulder, Colo. 80302; Partners in Health (identify Haiti), P.O. Box 996, Frederick, Md. 21705, and Women for Women International, P.O. Box 9224, Central Islip, N.Y. 11722.