J. Reilly Lewis. (Courtesy of Washington Bach Consort/Courtesy of Washington Bach Consort)

J. Reilly Lewis, an organist and conductor who founded the Washington Bach Consort and spent three decades as the music director of the Cathedral Choral Society, becoming one of the most prominent figures in Washington’s classical music circles, died June 9 at his home in Arlington, Va. He was 71.

The cause was sudden cardiac arrest, said Margaret Shannon, a spokeswoman for the choral society.

Much of Dr. Lewis’s career revolved around two great edifices: Washington National Cathedral and the music of Johann Sebastian Bach. He first performed at the cathedral when he was 8, as a member of the junior boys choir. He became music director of the Cathedral Choral Society, a 145-voice choir that rehearses and often performs at the cathedral, in 1985. He was scheduled to lead a singalong performance at the cathedral on Sunday.

Dr. Lewis became so popular among D.C.-area music aficionados that he was featured on a bobblehead doll.

“Not only was he a fantastic musician, he was always this magnetic, charismatic personality,” Marc Eisenberg, executive director of the Washington Bach Consort, said Saturday in an interview. “He was absolutely a musical genius. There isn’t another Reilly Lewis walking around.”

J. Reilly Lewis. (Marvin Joseph/The Washington Post)

After becoming enchanted with Bach’s music at age 12, Dr. Lewis went on to become a virtuoso organist and a leading interpreter of the complex music of the 18th-century German composer.

In the 1970s, Dr. Lewis and several friends began meeting in the basement of his mother’s house in Arlington to play the music of Bach. As the informal group began to draw a following, Dr. Lewis formally launched the Washington Bach Consort in 1977.

In time it came to be recognized as one of the country’s premier baroque-music ensembles, with an emphasis on historically authentic performances on instruments from Bach’s era.

The ensemble presented all of Bach’s more than 200 cantatas, as well as works by other baroque composers, went on three international tours and released several recordings.

“Over the last two decades,” Washington Post contributor Cecelia Porter wrote in 1998, “conductor J. Reilly Lewis has raised this group to a world-class ensemble even compared with the finest groups in Bach’s native land.”

Dr. Lewis, who was the Bach Consort’s artistic director until his death, often conducted from the harpsichord and performed on organ at the group’s concerts, including free monthly performances at the Church of the Epiphany in downtown Washington.

With the Cathedral Choral Society, Dr. Lewis molded a group of volunteer singers into a versatile vocal unit, performing not just classical masterpieces but also Christmas music and new compositions. He occasionally led the group in collaborations with the National Symphony Orchestra. In April, he conducted the rousing music of Carl Orff’s “Carmina Burana” at the Kennedy Center in a Washington Ballet production.

Dr. Lewis was known for his deft touch at bringing out the best in his singers without belitting them if they fell short of his expectations.

“In my 22 years, I never remember him embarrassing anyone personally,” Kathy Welling, a member of the alto section, said Saturday. “That just would not be Reilly. It was always about the integrity of the music.”

Dr. Lewis’s gentle manner was captured in a 2011 Washington Post article as his singers struggled to learn a new piece of music.

“Diction. Pacing. Rhythm,” he said. “Bring that melody out. Tenors and bass, stand. Sopranos, let’s keep this a covered veil. . . . You’ve got to anticipate. A little more exuberance. A little more bounce to the word ‘sing.’ That’s good. Don’t get louder. . .­ . Let’s do it again until you learn to love it.”

John Reilly Lewis was born Sept. 15, 1944, at Mare Island, Calif., where his father was stationed as a naval officer. The family settled in Arlington, and Dr. Lewis was drawn to music from an early age.

After attending a boarding school in Peekskill, N.Y., he graduated in 1967 from Oberlin College in Ohio. He then attended the Juilliard School in New York, receiving a master’s degree in 1969 and a doctorate in musical performance in 1977.

In 1969 and 1970, he studied in Germany with organist Helmut Wacha on a Fulbright scholarship. He spent the summer of 1975 studying in France with the renowned music teacher Nadia Boulanger.

From 1972 until his death, Dr. Lewis was the organist and choirmaster at Clarendon United Methodist Church in Arlington.

“He very much viewed himself as a church musician, as Bach did,” said Todd Fickley, his musical assistant at both the Cathedral Choral Society and the Washington Bach Consort.

An early marriage ended in divorce, as well as his second marriage, to Kaaren Lynn Ray. Survivors include his wife of 18 years, Beth Van Wagoner Lewis of Arlington; a daughter from his second marriage, Lauren Currie Lewis of New York; and a grandson.

In 2011, as a concert approached for the Cathedral Choral Society, Dr. Lewis was helping his singers master an unfamiliar work.

“Once more from the beginning,” he said. “Put your music down and take a chance. Pounce on it! . . . Let’s have the altos. Sopranos, don’t let them blow you down. Now, second sopranos. First altos. You got it! C-sharp. See, it’s a piece of cake.”