Scott Johnson, a composer and guitarist who forged an original style involving the rhythmic cadences of speech and the gestures and timbres of popular music, died on Friday in Manhattan. He was 70.

Mr. Johnson’s sister Susan Lee Johnson said the cause was complications of aspiration pneumonia. Mr. Johnson had also been diagnosed with lung cancer in May 2021.

Mr. Johnson immersed himself in music and art from an early age and played in rock bands in high school. His artistic breakthrough came with “John Somebody,” a playfully inventive work for solo electric guitar with taped accompaniment, which he assembled from 1980 to 1982, and which, as performed regularly and recorded in 1986, won him considerable acclaim.

To create that work, Mr. Johnson transcribed into approximate musical notation portions of a friend’s telephone conversation he had recorded in 1977 (“You know who’s in New York? You remember that guy, John somebody? He was a … he was sort of a…”), along with other snatches of speech and laughter.

Mr. Johnson added dense layers of guitar, saxophone and percussion, and a virtuosic solo part for live guitarist, with pitches, melodic motifs and rhythms derived from the recorded vocalism. The result mixed the structural rigor of classical composition with the ebullient sound and attitude of rock.

“To these ears, the music mirrors the subterranean rumble, the welter of voices and other overlaid sounds of the city, with the cries of superamplified guitars hovering like angels above the fray,” Robert Palmer of The New York Times wrote about “John Somebody” in 1986. “It’s a compelling marriage of rock elements and classical formalism that doesn’t shortchange either.”

Mr. Johnson refined and extended the process he developed for “John Somebody” in several subsequent works. He also created purely instrumental works and, for a time, led an ensemble comprising three saxophonists, two electric guitarists, an electric bass guitarist and two drummers.

The technical demands of Mr. Johnson’s music could make collaboration a daunting prospect. But he formed close bonds with younger artists and groups like the Bang on a Can All-Stars, Alarm Will Sound and the guitarist and composer Mark Dancigers, who came of age at a time when fluency in rock and pop idioms became more prevalent among concert-music composers and performers.

“He was a player who embraced complexity,” Mr. Dancigers said in a phone interview. “The writing is challenging from a number of perspectives: There are leaps, there are rapid virtuosic passages, there are chord voicings that change very rapidly.”

Mr. Dancingers suggested that Mr. Johnson’s compositions paved the way for younger composers similarly inclined toward hybridity. “The first time I heard him present his music,” he said, “I thought, this guy’s a little ahead of his time.”

Scott Richard Johnson was born in Madison, Wis., on May 12, 1952. His father, Robert Warren Johnson, worked in marketing, merchandising and sales positions for a battery company. His mother, Janet Mary (Stecker) Johnson, was a homemaker. They both belonged to a church choir and attended concerts by the local symphony orchestra.

Intellectually inquisitive and artistically inclined, Mr. Johnson played clarinet before switching to electric guitar in high school. An early infatuation with folk groups like the Kingston Trio ceded to a passion for Jimi Hendrix and the Rolling Stones.

“His bands practiced in the family basement,” his sister Susan wrote in an email, “and the practice sessions shook the house.”

Hearing Stravinsky’s ballet “The Rite of Spring” sparked Mr. Johnson’s interest in modern classical composition. By college, he wrote in a biography on his website, “I was studying music theory during the week and playing in bars on the weekends.”

Daunted by the serialist compositional style that held sway in academia, Mr. Johnson turned to visual art. He graduated from the University of Wisconsin–Madison with a bachelor’s degree in art in 1974 and then drove a cab in Madison for a year to finance his move to New York City in 1975.

By that time he had temporarily set music aside. But he quickly established himself among a rising generation of versatile, inquisitive Downtown creators, including the composers Rhys Chatham, Peter Gordon and Arthur Russell, the choreographer Karole Armitage and the interdisciplinary artist Laurie Anderson, with all of whom he collaborated.

On arrival, Mr. Johnson supported himself by demolishing and renovating lofts with a friend from Madison, Scott Billingsley, later known as the filmmaker Scott B. He also joined Mr. Gordon’s Love of Life Orchestra.

“It sometimes took Scott days to be able to use his fingers for guitar, after sanding floors all day” Mr. Gordon said by email. Like many other downtown composers, including Mr. Gordon, Mr. Johnson also worked as a tape editor for the sound artist and performer Charlie Morrow.

Tape played a key role in Mr. Johnson’s oeuvre. For the earliest work he acknowledges on his website, “Home and Variations” (1979), he manipulated the voices of members of a dance company to accompany a dance.

In the liner notes he wrote for a 2004 reissue of “John Somebody” on John Zorn’s Tzadik label, Mr. Johnson said that germinal material for the piece dated as far back as 1977. At that time, he had to cut up strips of magnetic tape and then tape them back together. One particular passage in the work, he recounted, required a tape loop 25 feet long.

Addressing the work’s development in a 2018 interview for the web publication NewMusicBox, Mr. Johnson cited several inspirations: early tape works in which Steve Reich looped and layered recorded speech, the call-and-response convention fundamental to the blues, and compositions in which Olivier Messiaen transcribed and notated bird song. In turn, “John Somebody” announced a signature style that anticipated Mr. Reich’s landmark 1988 piece “Different Trains,” and had a strong influence on other composers.

Despite the seeming novelty of his approach, Mr. Johnson asserted his alliance to a historic lineage of rigorous formal composition. In his view, bringing elements of rock into the concert-music world extended a tradition of composers borrowing from vernacular styles, like folk songs. “John Somebody,” he wrote, resulted “when the partially developed elements laid out on my table met the animating idea of the Baroque dance suite, episodic but unified.”

Mr. Johnson performed the work regularly. A 1986 recording made for the upstart record company Icon benefited from a partnership with Nonesuch, a more established label whose cachet was growing, and the commercial clout of that label’s corporate parent, Warner Bros.

Mr. Johnson’s score for the 1988 Paul Schrader film “Patty Hearst” was released on Nonesuch. So were portions of “How It Happens” (1991-93), an evening-length composition for the Kronos Quartet with the recorded voice of the political commentator I.F. Stone, scattered across three different albums.

Mr. Johnson, increasingly used his speech-manipulation technique to address social and philosophical concerns. In “Americans” (2003), he sampled the speech of immigrants recorded in Queens to examine cultural isolation and assimilation. For “Mind Out of Matter” (2009-15), a 75-minute work for Alarm Will Sound, he employed the voice of the philosopher Daniel Dennett, who has examined the history of religion.

The Alarm Will Sound conductor Alan Pierson grew familiar with Mr. Johnson’s exactitude while preparing “Mind Out of Matter.” The percussion parts included some nearly impossible passages, and at one point players suggested altering a few notes.

“Even as a conductor and a listener, I’m thinking you’re probably not even going to hear those notes,” Mr. Pierson said by phone. “But having to rethink that was so intense for Scott. Watching the amount of attention that he would put into reconsidering just a couple of notes, in a passage where there was so much going on, was really something to see.”

In addition to his sister Susan, Mr. Johnson is survived by another sister, Lynne Ann Johnson. His wife, Marlisa Monroe, a classical-music publicist, apparently died on Friday: A Police Department spokesperson confirmed on Saturday that a 70-year-old woman was found unconscious and unresponsive, and later pronounced dead, at the Manhattan address where Mr. Johnson and Ms. Monroe lived. No cause of death has yet been determined; an investigation is ongoing.

In his last months, Mr. Johnson completed a final composition: a wholly acoustic work for string quartet and mezzo-soprano. The piece, titled “Map,” features an elegiac text by Mr. Johnson, which reads in part:

Every route is a branching fate
well worn path or departure
shared inherited highways
engineered exits
or unmarked dirt swerves
accidents, errors, discoveries.