Grace Griffith, a Washington-area singer whose clear and graceful voice made her a beloved figure in the region’s folk and Celtic music scenes, and who helped launch Eva Cassidy to posthumous fame by sharing her music with a small West Coast record label, died June 5 at a nursing center in Sandy Spring, Md. She was 64.

The cause was complications of Parkinson’s disease, said her brother Joe Sisson. Ms. Griffith had been diagnosed with early-onset Parkinson’s in 1998 and continued to record for nearly two decades, even as the degenerative disorder limited her singing and forced her to stop playing the guitar, whistle and dulcimer.

Fans and collaborators of Ms. Griffith often spoke of her music’s ethereal, even spiritual quality, what Blix Street Records President Bill Straw described as her “healing sound.” It was fitting for an artist who worked as a physical therapist by day — treating patients in La Plata, Md., at the hospital where she was born — and as a musician by night, playing at nearby folk venues and Irish clubs.

“If you put on earphones, or turn the speaker up and close your eyes, her music is like meditation,” Straw said in a phone interview. “The closest thing I’ve heard to Grace in terms of timbre would be Judy Collins.”

Ms. Griffith toured only once, according to her longtime collaborator Marcy Marxer, and never had a hit record. But her local performances, as well as albums she released as a solo artist and member of folk and Celtic bands such as Connemara, made her a celebrated member of the D.C. music community, which honored her with more than a dozen Washington Area Music Association Awards.

In the liner notes for her final solo album, “Passing Through” (2014), former Washington Post music critic Richard Harrington wrote that Ms. Griffith “always had the purest instinct for songs that address universal themes of love and compassion, connection and community, spiritual aspiration and earthly determination.”

Her admirers included Emmylou Harris, Linda Ronstadt and a Maryland native named Eva Cassidy, who sang folk, jazz, pop and gospel songs while baffling record label executives with her range. In early 1996, soon after recording a live album at Blues Alley in Georgetown, Cassidy learned she had cancer that had spread to her bones. She died that November at age 33, all but unknown outside Washington.

Over the next several years, her covers of “Fields of Gold” and “Over the Rainbow” became radio hits in Europe and the United States, turning Cassidy — by many accounts shy and reluctant to perform — into an almost mythical figure. Once rejected by Blue Note Records, she found a posthumous home at Blix Street, based in Gig Harbor, Wash., which discovered her through Ms. Griffith.

The two singers had recently become friends when Ms. Griffith released “Grace” (1996), her first album with Blix Street. About six weeks before Cassidy’s death, Ms. Griffith called Straw at his home in Los Angeles. “We have this wonderful nightingale I’m afraid we’re going to lose,” he recalled her saying. “Can I send you a tape?” A few days later, he received a copy of Cassidy’s live recording. “The moment I listened to that tape,” he later told the New York Times, “I knew this was one of the best singers I’d ever heard.”

Ms. Griffith arranged a meeting between Straw and Cassidy’s parents at her home in Accokeek, Md., paving the way for a record deal. “It was Grace’s perception and selflessness that made it possible,” Straw said on Wednesday. “I don’t think there’s any way we would have found Eva Cassidy if Grace hadn’t introduced us to her.”

Over the next two decades, Cassidy’s albums would sell more than 10 million copies, a startling figure for a singer who — like Ms. Griffith — preferred to play at small, intimate venues, according to her producer Chris Biondo.

“I think if Eva had a career it would have been like Grace’s,” Biondo said by phone. “She looked at Grace as a role model.”

The eighth of 10 children, Grace Bernadette Sisson was born in La Plata on Oct. 30, 1956, and grew up on a small farm in nearby Bryans Road. Her father worked in logistics for the federal government, and her mother was a homemaker. Both imparted a love of music to their children.

“To them singing was a free source of pleasure, and a way to pass one’s time while cleaning or just sitting,” Ms. Griffith wrote in a biographical note on her website. “I found my voice in the woods and the back pasture.” When she was about 12, she began singing at local coffeehouses, accompanying herself on guitar.

Encouraged by her parents to seek a more stable career, she studied physical therapy at the University of Maryland at Baltimore, graduating in 1978. Within a few years, she was performing again, singing with an Irish folk revival band called the Hags. She later formed the folk duo Hazlewood with singer-songwriter Susan Graham White and played with groups including the Greater Beltway Broads, which The Post once described as “a Celtic/cowgirl/kitchen-sink sextet.”

Ms. Griffith first showed signs of illness while working on her solo album “Minstrel Song” (2000) with Marxer, a Grammy-winning musician who produced several of her records. “I said, ‘Do you want me to take you to doctors’ appointments or finish your record?’ ” Marxer recalled. “She said, ‘Finish my record.’ ”

Ms. Griffith spoke and performed at events for people with Parkinson’s disease, including the first World Parkinson’s Congress, held in Washington in 2006. Around that time, she also underwent a neurological treatment known as deep brain stimulation, which restored her ability to play the guitar and, at least for a few years, helped her sing.

Biondo, who produced Ms. Griffith’s last several albums, said that she would delay taking her Parkinson’s medication while in the studio; the medicine created problems with her voice, even as it reduced her pain. “At the point where she couldn’t take it anymore, she took her medicine,” he said.

In her final public performance, Ms. Griffith sang in 2014 from a wheelchair at the Birchmere in Alexandria, Va., where she was accompanied by musicians including Marxer, Cathy Fink, Lisa Moscatiello, Tom Paxton and Al Petteway, who were able to finish songs if her voice gave out. Proceeds went toward Parkinson’s treatments that were not covered by her health insurance.

Her marriage to David Griffith ended in divorce. Survivors include her husband, Patrick Holmes, of Accokeek; two stepchildren; three brothers; and two sisters.

Ms. Griffith’s solo records included covers of songs such as Kris Kristofferson’s “A Moment of Forever” and Iris DeMent’s “My Life,” in which she reckoned with her own mortality — “My life, it’s only a season” — while finding comfort in bringing joy to others.

“In a way, I’m singing to myself,” she told The Post in 2006. “I need reassurance that love is on our side, that people are going to connect with you, that people who are angels are going to be there. I need to know that, so the lyrics are an affirmation of what the neurologists are saying in a more scientific way — that when you say something, you reinforce it into your mind.”

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