It’s usually not a good sign when video of a senior government official singing goes viral on social media, where the crowds are as tough as they come.

But when Secretary of State Antony J. Blinken picked up a black Fender guitar at a State Department event on Wednesday night and joined a band for Muddy Waters’s “Hoochie Coochie Man,” the response on X, the site formerly known as Twitter, where the video has been watched more than eight million times, drew positive reviews — and more than a little shock.

“I had. NO. Idea,” said one X user, who used an expletive to express her amazement, in the video’s most-viewed reply.

To be sure, there was also snark of the don’t-quit-your-day-job variety, and some tut-tutting about decorum (“Ukraine is on fire and Blinken is playing the guitar,” one user said). But on the whole, Mr. Blinken’s soulful baritone and crunchy blues chords, showcased at an event promoting a State Department “music diplomacy” initiative that was attended by Foo Fighters frontman Dave Grohl, escaped the dreaded label of cringecore.

Perhaps more interesting was the understandable surprise that America’s top diplomat has a rock ’n’ roll bone in his body. Mr. Blinken, 61, is unfailingly soft-spoken and so formal that he wore his suit jacket — buttoned, no less — for the jam.

Music is Mr. Blinken’s greatest nonpolitical passion. He once told Rolling Stone magazine that “the thread that runs throughout my life is probably music,” and said that hearing his parents play “A Hard Day’s Night” by the Beatles as a child was a thunderbolt that has defined him ever since. “I remember being absolutely hooked,” Mr. Blinken said in an interview last week.

His great guitar love is Eric Clapton, whom Mr. Blinken reports having seen live about 75 times.

Mr. Clapton’s bluesy style and frequent covers led Mr. Blinken to discover the electric blues greats like B.B. King, Otis Rush and Luther Allison. One of them discovered him back: While living in Paris with his family at the age of 16, Mr. Blinken worked his way to the front of the stage during a performance by Mr. King, singing along with the lyrics he had memorized completely.

“He sees me, I guess, and at the end he comes to the edge of the stage and bends down, and gives me his guitar pick,” Mr. Blinken said, sounding as though his mind remains slightly blown.

As a young man, well before people called him “Mr. Secretary” and bodyguards followed him everywhere, Mr. Blinken played in bands and collected at least a half dozen guitars, including a high-end Martin acoustic “that I don’t deserve,” he said. Years of noodling at home with a four-track culminated in his release of three singles on Spotify, under the moniker Ablinken. (Say that out loud slowly for dad-joke effect.)

The Spotify songs, which have collectively been streamed about 150,000 times — watch out, Harry Styles — show off a blues-rock sound with Everyman lyrics that bear no relation to the government official who talks about multilateral engagement and “diplomatic variable geometry.” (“And then I came home to you/But you said, ‘Let’s just be friends, yeah’” he sings over staccato electric chords in “Lip Service.”)

Mr. Blinken noted that he had recorded and uploaded the songs between 2018 and 2020, during the Trump era, when he was out of government and unsure whether he would return. “I had little idea that there would be another run at government, or a public career of any kind,” he said. “And so when the president put me forward for this job, there they were.”

The songs, which he has labeled “wonk rock,” occasionally pop up in his official life. They have been blared from speakers at overseas events, including before he addressed embassy employees in San José, the capital of Costa Rica, in June 2021. A Finnish radio station broadcast one when Mr. Blinken visited Helsinki in June to deliver a speech about the war in Ukraine.

Mr. Blinken’s former band, which has played under the name of Cash Bar Wedding, was pretty cool, at least by the standards of Washington. His bandmates included Eli Attie, a former speechwriter for Vice President Al Gore who went on to be a writer for “The West Wing,” and Jay Carney, a onetime spokesman for President Biden when Mr. Biden was vice president.

Mr. Carney called the band mostly “an excuse to hang out and talk about music.” But the group was serious enough to take semiregular trips to music meccas like New Orleans, booking studios for a day of writing and recording songs.

“As to the quality of the songs we created, let’s just say, mistakes were made!” said Mr. Carney, now head of policy and communications for Amazon. They have jammed with indie-rock legends like Alex Chilton of Big Star, Grant Hart of Hüsker Dü and Aimee Mann.

“Tony is actually a fine guitarist and songwriter,” Mr. Carney said. “We’re worried his State Department gig is a sign that he’s ditching us to launch a solo career.”

Many foreign diplomats and leaders have clearly done their homework: No fewer than eight have given Mr. Blinken guitars or accessories like guitar straps as customary gifts (which he must purchase if he wants to keep). From Israel’s foreign minister, Eli Cohen, came a blue acoustic guitar with an engraving of U.S. and Israeli flags. Another guitar was offered by Qin Gang, the Chinese foreign minister who mysteriously disappeared this summer.

In an interview, Mr. Blinken recalled a special rapport with Japan’s former foreign minister, Yoshimasa Hayashi, a skilled pianist, guitar player and Beatles nut. “We totally bonded over music,” Mr. Blinken said, calling it “a constant refrain in our diplomatic discourse.”

That discourse could get nerdy. Invoking a famous Beatles track, Mr. Blinken recalled “bad pun references like, ‘This policy’s going to be a long and winding road.’”

In April, Mr. Hayashi hosted a meeting of the Group of 7 foreign ministers in Hiroshima, Japan. When the ministers convened one evening after official business was concluded, Mr. Blinken produced a small travel guitar he sometimes takes on foreign trips. Mr. Hayashi brought his own. With the help of a karaoke machine, they strummed chords as the other ministers, briefly forgetting matters like Ukraine and climate change, joyously sang along.

“It’s a wonderfully bonding thing to forget about the weight of the world for a couple of hours and come together just as friends with a common passion for music,” Mr. Blinken said.

He noted that the United States has used music as a diplomatic tool for decades. Amid competition with the Soviet Union for global influence in the 1950s, the State Department sponsored foreign tours for jazz greats like Dizzy Gillespie, Quincy Jones, Louis Armstrong and Ella Fitzgerald.

Today’s version lacks that star power: Mr. Blinken’s new initiative includes a mentorship program for foreign music professionals that works in partnership with the Recording Academy, the organization that stages the Grammy Awards. English classes taught abroad by the State Department, which are hugely popular overseas, will now incorporate popular music lyrics.

“Music is the most powerful connecter,” Mr. Blinken said. “It transcends virtually any kind of barrier you can think of.”