Robert Plath, a Mill Valley lawyer who founded an organization called the Worldwide Forgiveness Alliance and launched an annual International Forgiveness Day, died Nov. 13 at St. Mary’s Hospital in San Francisco after a brief illness. He was 89.

Mr. Plath, who believed that practicing forgiveness leads to better health and relationships, served as executive director of the Forgiveness Alliance for 17 years before stepping down in 2013. He was honored that year at the annual Forgiveness Day at Dominican University.

“I realize now how one life can make such a big difference,” said Jacinta Martin, executive director of the Forgiveness Alliance. “We will miss this amazing man and the incredible passion he brought to his mission, to bring the healing power of forgiveness to this planet.”

Mr. Plath founded the Forgiveness Alliance and Forgiveness Day, celebrated each year on Aug. 2, after being inspired by “A Course in Miracles,” a book by Helen Schucman designed to bring about “spiritual transformation.”

At the 13th annual International Forgiveness Day in 2009, the keynote address was given by Rep. John Lewis, a Georgia Democrat and prominent civil rights pioneer. Mr. Plath reached out to the congressman after he publicly accepted an apology from former Ku Klux Klansman Elwin Wilson, who had beaten him during a civil rights demonstration in South Carolina in 1961. Wilson also appeared at the event, held at Dominican University in San Rafael.

“In the civil rights movement, our struggle was against bad laws and unfair customs, not against human beings,” Lewis said. “Forgiveness is very much in keeping with the discipline and philosophy of nonviolence.”

Born in 1926, Mr. Plath grew up in Grosse Pointe, Michigan, a suburb of Detroit. At the University of Michigan, he played on the football and baseball teams. After graduation, he played football on a semi-pro team.

After a stint in the Coast Guard, he earned a law degree from the Hastings School of Law in San Francisco, working his way through school as a janitor on campus along with his classmate and friend, Willie Brown, who would go on to become speaker of the state Assembly and mayor of San Francisco.

As a newly minted attorney, Mr. Plath became a protege of San Francisco lawyer Vincent Hallinan, a prominent liberal who ran for U.S. president in 1952 as a Progressive Party candidate. He later went into private practice, earning a reputation as a defender of the little guy against big government and large corporations and was a leader of the 1965 boycott of Chrysler Corp. when the company was accused of racial discrimination.

After the 1964 murders of civil rights workers James Chaney, Andrew Goodman and Michael Schwerner during “Freedom Summer” in Mississippi, Mr. Plath and 19 other lawyers spent two months in the state, taking witness depositions in the case against the Klansmen eventually convicted of the killings. The case led to the passing of the 1964 Civil Rights Act.

A Marin resident since 1955, Mr. Plath was a founding board member and director of the nonprofit Veterans Housing and Services. He traveled in the U.S. and China for a year and a half, crusading for more humane birthing practices advocated by Dr. Frederick Leboyer in his book “Birth Without Violence.”

In 2000, Pope John Paul II gave Mr. Plath an apostolic blessing for his Day of Forgiveness.

He is survived by sisters Mary and Helen, both residents of Michigan.

A public memorial is being planned.