Esa-Pekka Salonen, the coolly brilliant Finnish conductor and composer who is among the world’s most dynamic, versatile and celebrated musical figures, has been named the next music director of the San Francisco Symphony.

Salonen, 60, will succeed Michael Tilson Thomas at the conclusion of the 2019-20 season, when Thomas steps down after 25 years at the orchestra’s helm. It’s an appointment that has the potential to write an innovative new chapter in the orchestra’s 107-year history, and even to forge an influential path for classical music in the 21st century.

Salonen spent 17 years as music director of the Los Angeles Philharmonic, helping shepherd it to its current position as one of the nation’s most inventive and highly regarded orchestras. Yet in 2009, when he stepped down from the orchestra to concentrate on composing, he stated — and has repeated in the ensuing years — that he had no interest in another music director job.

Clearly, something changed his mind.

“There were two things,” he said in a recent interview with The Chronicle. “The more important one was that it’s this orchestra in this city, and the chance to continue Michael’s work.

“The second one is just the timing. This approach came right when I’d begun to think that maybe there would be one more opportunity for me in the way of conducting.”

Perhaps even more significantly, Salonen said, he and the San Francisco Symphony are eager to start working together to rethink all the assumptions that shape the world of orchestral music. Both Salonen and the Symphony see the opportunity to create a laboratory for reimagining classical music.

“My problem has never been with the material itself, with the actual content of what we play. But I think the worst thing we could do to our art form is to assume that everything is going to be like this forever, and therefore we don’t have to do anything,” Salonen said.

“It’s very clear to everyone in this business that things are changing, and that certain ideas that were completely solid 20 years ago, say, no longer are. And I was inspired by the idea of leading an organization that is curious and interested and willing to look into the future — not in a reactive way, but wanting to be in the driver’s seat whatever the change may be.”

For the Symphony’s search committee, which included board members, orchestral musicians and representatives of management, Salonen was always a leading candidate, according to CEO Mark C. Hanson.

“The committee developed a general profile of who we wanted,” Hanson said. “Someone with great musicianship, someone highly motivated to make the San Francisco Symphony the defining moment of their career, with a creative and unique vision of what the orchestra can be not only today but in the future.

“From the beginning, Esa-Pekka was right up there among the top candidates. And that inspired us to get in front of him and at least begin a conversation.”

In August, a delegation of musicians and board members visited Salonen in London, where he was conducting the Philharmonia Orchestra. (He has been that orchestra’s principal conductor and artistic adviser since 2008, but he will give up the post when he comes to San Francisco.)

“He’s always been one of the top names on the surveys that the orchestra musicians fill out about guest conductors,” said violinist Melissa Kleinbart, the chair of the players’ committee and a member of the search committee. “But going into this process, no one assumed he was even interested.”

The fact that orchestral musicians had been active in the search made the San Francisco Symphony’s case that much more persuasive.

“I liked that it was not just the management and the board, but the orchestra too – the people who actually do the work,” Salonen said. “That’s what this is really about: what happens between the musicians and the conductor on stage night after night.”

Salonen has been ranked among the world’s most important and energetic musical figures pretty much since the moment he first came on the scene in 1983 as a last-minute stand-in for, of all people, Michael Tilson Thomas. His performance in London of Mahler’s Third Symphony with the Philharmonia Orchestra excited international interest in him and ultimately led to his appointment in Los Angeles at age 34.

During his time in Southern California, Salonen established himself as a conductor, composer and orchestra builder of rare energy and versatility. His performances of a wide range of orchestral and operatic repertoire, documented in a discography of several dozen recordings, are marked by crisp technical mastery, sleek precision and expressive urgency.

His orchestral compositions, many of them premiered by the Los Angeles Philharmonic, are colorful and dramatic, rooted in European modernism but infused with a freshness and freedom that grew out of his American sojourn. And his tireless organizational leadership in Los Angeles — including helping to oversee the 2003 opening of Walt Disney Concert Hall — propelled the Philharmonic to the forefront of the American orchestral world.

Salonen has been a guest conductor with the San Francisco Symphony three times, beginning in 2004 as part of an all-California “conductor swap” that also saw Thomas guest-conducting the L.A. Philharmonic. In that program, Salonen conducted his dark orchestral tone poem “Insomnia.” He returned to Davies Symphony Hall in 2012 to conduct his Violin Concerto with soloist Leila Josefowicz, and again in 2015.

“Every time I came back, the communication with the musicians was better,” Salonen said. “They’re very quick, very flexible and ready to tackle anything.

“Also, they’re good people, which is surprisingly important in this field — because if you don’t like them and yet you sign up for X number of years, that’s not a very good starting point.”

In a statement, Thomas said, “I am so happy that my friend and colleague is coming to San Francisco. Our lives have been personally and musically intertwined for years and we share many musical values. We both deeply love music and the people who make the music. It will be a joy to collaborate with him on this bright future for the whole Symphony family.”

Salonen will start with a five-year contract and a salary that Hanson would describe only as “competitive.” The plan is for him to conduct a couple of weeks during the 2019-20 season — Thomas’ last as music director — then lead the orchestra for six weeks (and an Asian tour) during his first season as he works through other commitments.

Beginning with the 2021-22 season, the Symphony said, Salonen will conduct 12 to 14 weeks a year.

But San Francisco audiences need not wait that long to hear him. Salonen is scheduled to conduct the orchestra next month, on Jan. 18-20, filling a slot vacated by Lithuanian conductor Mirga Grazinyte-Tyla. The program will include a 2018 piece by the acclaimed Icelandic composer Anna Thorvaldsdottir, as well as music by Sibelius and Richard Strauss.

Beyond that, Salonen is gearing up to explore ways of revitalizing the concert experience, a ritual that he feels has become stale and predictable.

He’s a self-described “tech geek” (a widely viewed iPad commercial showed him using the device to compose his Violin Concerto while globetrotting), and he’s excited about the proximity of Silicon Valley.

The initiatives he has spearheaded in Los Angeles and London include a range of multidisciplinary approaches involving lighting, dance, theater and virtual reality.

“Sometimes I read about myself as some kind of progressive,” he said, “and it’s surprising because I think the things I’m doing are normal.”

One of Salonen’s first steps has been to assemble a collection of younger artists, in music and related fields, with whom he can consult and collaborate on ambitious projects. They include such figures as soprano Julia Bullock, composer Nico Muhly, bassist-composer Esperanza Spalding and flutist Claire Chase.

“One of the big challenges for a symphonic organization is to be in touch with what’s going on,” Salonen said. “I have a healthy self-confidence, but I’m also realistic, and I realize that there’s no natural way for me to get to know what’s going on other than by talking to people who do.”

Salonen is one of a generation of prominent Finnish composers that also includes Kaija Saariaho and Magnus Lindberg, school chums from Helsinki who remain his close friends and creative sounding boards. His plan had been to pursue a career solely as a composer, but the substitution in 1983 launched his conducting career overnight. Salonen served as principal conductor of the Swedish Radio Orchestra from 1985 to 1995, and he recently concluded three seasons as composer in residence with the New York Philharmonic.

Salonen and his wife, a former orchestral violinist, separated last year, and his three children are located across the United States. Ella, 26, lives in New York and works for a company that makes equipment for rock guitars; Anja, 24, is a painter in Los Angeles; and Oliver, 19, is a sophomore at the University of Chicago. Salonen currently lives in Brooklyn, midway between his children and his 90-year-old mother in Helsinki, but says he plans to take up full-time residence in San Francisco.

“I don’t actually know this city very well. I’ve been here maybe 10 times over the years, usually just for a day or two at a time, maybe a week,” he said. “So I’ve got a lot of learning to do.”