NASHVILLE — Sonny Osborne, the banjo player and singer who, with his older brother, Bobby, led one of the most innovative and beloved bands in bluegrass music, died on Sunday at his home in nearby Hendersonville, Tenn. He was 83.

His death, after a series of strokes, was confirmed by his friend and protégé Lincoln Hensley.

Best known for their 1967 hit “Rocky Top,” the Osborne Brothers pioneered a style of three-part harmony singing in which Bobby Osborne sang tenor melodies pitched above the trio’s other two voices, instead of between them, as was the custom in bluegrass. Sonny Osborne sang the baritone harmonies, with various second tenors over the years adding a third layer of harmony to round out the bright, lyrical blend that became the group’s calling card.

The Osbornes broke further with bluegrass convention by augmenting Mr. Osborne’s driving yet richly melodic banjo playing — and his brother’s jazz-inspired mandolin work — with string sections, drums and pedal steel guitar. They were also the first bluegrass group to record with twin banjos and, more alarming to bluegrass purists, to add electric pickups to their instruments, abandoning the longstanding practice of huddling around a single microphone.

Addressing the group’s critics in a 2000 interview with the music magazine No Depression, Mr. Osborne recalled the allegations of betrayal that were leveled against the band for “going electric” — censure redolent of that heaped on Bob Dylan for appearing with an electric band at the Newport Folk Festival in 1965.

“They thought, ‘Oh, they’ve changed, they did this, they did that, they’ve changed’ — well, we didn’t,” Mr. Osborne insisted. “We played the same things we normally played. We just added this stuff all around us.”

Despite — or perhaps because of — their unorthodox approach, the Osbornes emerged as one of the few bluegrass bands of the 1950s and ’60s to consistently place recordings on the country charts. In 1971 they were named vocal group of the year by the Country Music Association, a rare distinction for a bluegrass ensemble.

The Osbornes’ repertoire was as expansive as their sonic palette, encompassing “Old Kentucky Home,” by Randy Newman, and “Midnight Flyer,” a song written by Paul Craft (who also wrote the 1976 Bobby Bare hit, “Dropkick Me, Jesus”) and popularized by the Eagles shortly after the Osbornes recorded it in the early ’70s.

In 1968 they released “Yesterday, Today & the Osborne Brothers,” an album that connected bluegrass’s past with its future, broadening the idiom’s vocabulary while serving as a harbinger of intrepid inheritors like Newgrass Revival and Alison Krauss & Union Station.

The first side of the original LP consisted of traditional fare associated with the bluegrass patriarch Bill Monroe. The second side was steeped in material arranged in a more contemporary vein, including “Rocky Top,” a song written by the husband-and-wife team of Boudleaux and Felice Bryant (best known for their Everly Brothers hits).

A Top 40 country hit spurred by hurtling instrumental solos by both Osborne brothers, “Rocky Top” was later adopted as an official song by the state of Tennessee. Like “Tennessee Hound Dog,” another Top 40 country hit written for the Osbornes by the Bryants, “Rocky Top” was an unabashed paean to the mountain culture of the brothers’ childhood:

Rocky Top, you’ll always be
Home sweet home to me.
Good ol’ Rocky Top
Rocky Top, Tennessee
Rocky Top, Tennessee.

Sonny Osborne was born on Oct. 29, 1937, in Thousandsticks, an Appalachian enclave near Hyden, Ky., where he and his brother grew up. Their parents, Robert and Daisy (Dixon) Osborne, were schoolteachers; their father supplemented the family income by working in his parents’ general store.

Mr. Osborne took up the banjo at 11, after the family had moved to Dayton, Ohio. He and his brother started their own band in 1953, while Sonny, still in high school, also played briefly with Bill Monroe. In 1954 the brothers made a half-dozen recordings with the flamboyant bluegrass bandleader Jimmy Martin.

“We didn’t want to be farmers,” Mr. Osborne said in his No Depression interview. “Music was the only thing we wanted to do, that’s it.”

The Osbornes joined the WWVA Jamboree in Wheeling, W.Va., in 1956 and remained there for the rest of the decade. Among their most acclaimed recordings from this period were “Ruby, Are You Mad?,” a barnburner, featuring both Osborne brothers on banjo, written by the old-timey singer Cousin Emmy (a.k.a. Cynthia May Carver), and “Once More,” an old-fashioned love song. Both were released by MGM Records in the late 1950s and credited to the Osborne Brothers and Red Allen, who was featured on tenor vocals and acoustic guitar in early incarnations of the group.

The Osbornes became the first bluegrass band to perform on a college campus, appearing in 1960 at Antioch College in Yellow Springs, Ohio before taking their Appalachian “folk” music to places in the northeast like New York University and Club 47 in Boston.

The Osbornes signed with the Nashville division of Decca Records, then headed by the celebrated producer Owen Bradley, in 1963. A year later they joined the Grand Ole Opry. They also began bucking bluegrass tradition in earnest by, among other things, supplementing their performances with drums and dobro.

The Osbornes recorded extensively for Decca (which later became MCA) before they left the label in 1974, disappointed over not having had more than middling success on country radio. A return to a more traditional approach rejuvenated their career, securing their reputation over the next three decades as bluegrass elders alongside giants like Flatt & Scruggs, Mr. Monroe and the Stanley Brothers. They were inducted into the International Bluegrass Music Association’s Hall of Fame in 1994.

Mr. Osborne retired from performing in 2005 after suffering a shoulder injury. He nevertheless remained active in bluegrass circles by promoting his own line of banjos and writing “Ask Sonny Anything,” a weekly column for Bluegrass Today that brimmed with the same energy and wit he had once flashed onstage.

Besides his brother, Mr. Osborne is survived by his wife of 63 years, Judy Wachter Osborne; his sister, Louise Williams; a son, Steven; a daughter, Karen Davenport; two grandchildren; and three great-grandchildren.

In 1965 Mr. Osborne began experimenting with a special tuning that gave his banjo a timbre redolent of that of an electric instrument, or even at times of horns or a steel guitar. What he discovered, fed by his omnivorous taste in music, did more than shape his approach to banjo-playing, which became more wide-ranging; it also shaped the sonic directions the Osbornes would take for the remainder of the decade — and beyond.

“The notes themselves came from constant listening to every other kind of music that you can imagine,” Mr. Osborne explained in 2000. “Steel guitars and electric guitars, horns, saxophone, trumpet, piano — if you listened to all that stuff, if you were to be a huge fan of the kind of music that I listened to, you’d hear a little bit of everything in there.

“There’s some of everybody in the notes that I played, but when you put them on the banjo, then it’s a whole different ballgame.”