Maestro Nikolaus Harnoncourt conducts the traditionel New Year's Concert of the Vienna Philharmonics in Vienna in 2003. (Leonhard Foeger/Reuters)

Nikolaus Harnoncourt, an Austrian conductor whose internationally renowned career first focused on a search for authenticity in baroque and other old music and later expanded into masterful interpretations across the classical spectrum, died March 5 in St. Georgen, Austria. He was 86.

His wife, Alice Harnoncourt, confirmed the death but did not specify the cause. He died less than three months after taking his last bow on the concert stage.

Born into a lineage that included some of Europe’s most aristocratic families, Mr. Harnoncourt was also part of Austria’s musical nobility, with mastery that put him on the level of other great postwar Austrian conductors Herbert von Karajan, Karl Boehm and Carlos Kleiber.

His concern for historical detail was legendary. He often distributed his own material to orchestras, adding expression marks on how to create more authentic or refined interpretations, aiming to erase what he called “traditionally traded” ­mistakes.

Adding period instruments as well as tempi and dynamics discarded by modern performances, Mr. Harnoncourt broke through in the 1970s from relative obscurity with a series of celebrated performances, particularly of Monteverdi and Mozart.

Austrian conductor Nikolaus Harnoncourt in 2006. (Urs Flueeler/EPA)

He thought of his conducting as alive and romantic, not a relic of history.

“I have always hated the word ‘authenticity’ because it is so dangerous,” Mr. Harnoncourt said. “ ‘Museum music’ does not interest me. I have no intention of organizing guided tours to visit Louis XIV or Johann Sebastian Bach.”

He later expanded his repertoire to include 19th-century opera favorites such as Verdi’s “Aida” but didn’t stop there. His individually accented interpretations, including composers as diverse as Beethoven and Richard Strauss already led Switzerland’s Neue Zuercher Zeitung newspaper in 1999 to call him “the protagonist of the new expressionism.”

His 2001 Grammy Award for a recording of Bach’s “St. Matthew Passion” was only one of dozens of honors reflecting his musical standing.

Mr. Harnoncourt believed art was the foil to modern society’s materialism, which he saw as a threat to Europe’s cultural values. As a boy, he acquired his knowledge of sacral music at the cathedral in Graz, Austria, where he grew up.

“We as musicians — indeed all artists — have to administer a powerful, a holy language,” Mr. Harnoncourt said in a speech for the Mozart Year of 1991, two centuries after the Austrian wunderkind’s death. “We have to do everything in our power to keep it from getting lost in the maelstrom of materialism.”

His last few years at the podium were marred by occasional cancellations because of failing health. Still, he was able to finish projects such as Jacques Offenbach’s “Barbe-bleue” and Henry Purcell’s “The Fairy Queen” at his Styriarte music festival in Austria.

His last public appearance was in January, through a video recording — and the message was typical Harnoncourt.

“I wish you not a nice evening but a stirring one,” he told the audience at the 10th-anniversary celebration of the relaunch Vienna’s Theater an der Wien from a musical stage to an opera house.

Nikolaus Harnoncourt was born in Berlin on Dec. 6, 1929. His father, Eberhard, belonged to the house of the Count de la Fontaine und d’Harnoncourt-Unverzagt of Luxembourg-Lorraine, and his mother, Duchess Meran and Baroness of Brandhofen, was a great-grandchild of Archduke Johann of ­Styria.

The family moved later to Graz, in the southern Austrian state of Styria, where Mr. Harnoncourt became an accomplished cello player. Also drawn as an adolescent to puppet theater, Mr. Harnoncourt ultimately chose music as his profession after hearing a radio recording of Beethoven’s Seventh Symphony under German conductor Wilhelm Furtwaengler.

He went to Vienna in 1948 to study and four years later started as a cellist with the Vienna Symphony Orchestra under chief conductor Karajan — a job he would keep until 1969.

But the young Mr. Harnoncourt already was experimenting with older sounds, having forged a group in 1949 with his future wife, Alice Hoffelner, and others for performances with period ­instruments.

In 1953, he founded the Concentus Musicus Wien as a platform for his work on Renaissance and baroque music, using period instruments — many of which he had to buy at his own expense — to counteract “stultifying, aesthetically sanitized music-making.”

“For musical instruments, we were willing to do almost anything,” Mr. Harnoncourt wrote of his life in the 1950s, when money was scarce.

Early performances were mostly private and critics were initially hostile, commenting on the lack of brilliance in the musical sound and on the shortcomings of the older wind instruments.

But the troupe’s reputation grew, especially after a recording of Bach’s Brandenburg Concertos in 1962. The repertoire expanded into Monteverdi works. First tours of the United States and England came in 1966 and of Germany two years later.

Leaving his cello behind, Mr. Harnoncourt made his debut at the conductor’s rostrum in 1972 with Monteverdi’s “Il ritorno d’Ulisse in patria” at the Piccola Scala in Milan.

A few years later, his breakthrough was complete after teaming with French director Jean-Pierre Ponnelle on a celebrated cycle of Monteverdi operas performed at the Zurich Opera House on period instruments, starting with “L’Orfeo” in 1976.

In the 1980s, Mr. Harnoncourt performed a series of Mozart operas — including “Don Giovanni” and the less regularly performed “Lucio Silla” and “Mitridate, re di Ponto” — that were equally popular and critically acclaimed.

In 1989, he completed an 18-year project to record the complete cycle of Bach cantatas with the Concentus Musicus Wien and conducted orchestras in Berlin, London, Vienna and other places around the world. He also recorded all nine Beethoven symphonies with the Chamber Orchestra of Europe.

While he became a regular in the 1990s at the Vienna State Opera and the Salzburg Festival, Mr. Harnoncourt remained selective, rejecting a position with a “renowned orchestra so as not to be constrained in his artistic development and freedom,” according to a biography on the website of the Styriarte Festival.

Despite often exhausting schedules or rehearsals and performances, Mr. Harnoncourt also found time to teach as a professor at the Salzburg Mozarteum from 1972 to 1993.

— Associated Press