Gene Scheer, an opera librettist, was at his home in Washington, Conn., on Wednesday, ostensibly working but really watching the inauguration, when two words fluttered out of the television and practically knocked him out of his chair.

“I can’t believe this!” he exclaimed out loud, even though he was alone.

Those two words were “American Anthem,” and President Biden was speaking them as he reached the climax of his inaugural address, in which he quoted the song at length and described it as “a song that means a lot to me.”

Mr. Scheer, 62, wrote that song.

“I was truly in shock,” he said.

The moment capped the perhaps unlikely transformation of a song that he had the audacity to call “American Anthem” into a bona fide American anthem. After the opera star Denyce Graves, a rich-voiced mezzo-soprano, debuted the song in 1998 at the Smithsonian Institution, before an audience that included the Clintons, she helped make it a feature at inaugurations and other ceremonial events. It took on a new life, and reached a new audience, when Norah Jones recorded it for the 2007 World War II mini-series, “The War,” which Ken Burns directed with Lynn Novick. Last year, Ms. Graves sang it as Justice Ruth Bader Ginsburg lay in state at the United States Capitol.

Now, an incoming president was citing it in his inaugural address.

It was not a turn of events Mr. Scheer ever would have expected.

The song was inspired by a book he had come across in 1997 while helping his parents move. His parents, retired schoolteachers, had met nearly half a century earlier while picketing a New York City Y.M.C.A. that refused to accept African-Americans. The book, “Miracle at Philadelphia,” by Catherine Drinker Bowen, was about the Constitutional Convention; Mr. Scheer’s father, Ray, had taught it to his social studies students in Newton, N.J., not far from the Pennsylvania border. Mr. Scheer read it, was inspired, returned to his 400-square-foot apartment on the Upper West Side of Manhattan and began writing.

“I wrote the song just thinking about what the country means to me and this balancing act between personal freedom and collective responsibility,” Mr. Scheer said. “There’s this kind of wrestling match going on.”

Originally, he envisioned it as a sort of country-pop tune, but he only knew the opera world. Mr. Scheer had studied at the Eastman School of Music in Rochester, N.Y., and had originally pursued a career as an opera singer — he is a baritone — before realizing that he was unlikely to hit the big time. “I was like a Triple-A baseball player,” he said. “I couldn’t quite hit the fastball when I got to the major leagues.”

So after writing “American Anthem,” he played it for Ms. Graves, an opera star, whom he knew from his occasional work at the Metropolitan Opera. She loved it. And ever since she first sang it, she has championed the piece, performing it on television, at President George W. Bush’s second inauguration in 2005 and more recently at the ceremony for Justice Ginsburg.

“I have wanted the world to know Gene for a really long time; he’s so gifted and so generous,” Ms. Graves said in an interview.

Mr. Scheer recalled getting a call from Mr. Burns, the filmmaker, who heard a recording of it while driving across the country.

“He said, ‘I’m doing this documentary on World War II, and I’d love to potentially use the song,’” Mr. Scheer said. “I was bowled over.”

But Mr. Burns told him that he didn’t hear it as an art song. Mr. Scheer replied that he hadn’t originally intended it to be one. Mr. Burns enlisted Ms. Jones to record it for “The War.”

“I was struck by the song’s message,” Ms. Jones said in a statement. “In a post-9/11 era, being ‘patriotic’ was polarizing. This song, however, transcended the mudslinging at the time. It carries such a beautiful sentiment, one that honors the past and commits to the work we have to do going forward. At its core, the song is aspirational.” It’s even more poignant today, she added, “when we are seeing such strong opposition to each other within our own country.”

“I think it really fits with President Biden’s message of unity and collaboration,” she said.

Last year, after singing the work at the service for Justice Ginsburg, Ms. Graves met with Vice President Kamala Harris, who was then a senator, and Mr. Biden, who told her how touched he was by the song, she recalled.

“I told him it was from my friend Gene Scheer,” she said. “When the president mentioned it in his speech, I nearly fell over. It’s a beautiful way to begin the new year.”

In recent years, Mr. Scheer has found success as an opera librettist: He wrote the librettos for Jake Heggie’s “Moby-Dick,” Tobias Picker’s “An American Tragedy,” and Jennifer Higdon’s “Cold Mountain”; and his works have been performed at the Met Opera, the Royal Opera House in London and on other prestigious stages.

But the success of this song, he said, felt more personal. When President Biden quoted it this week, it made him think of his parents, he said, and he wished they had lived to see the inauguration.

“When Biden did this, it felt like I was connecting to my folks in a very meaningful and visceral way,” he said, adding that his mother would have been “ecstatic” to see Ms. Harris become vice president and that his parents “would have championed everything Biden was saying.”

Which included these words, from their son’s song:

The work and prayers of centuries

Have brought us to this day

What shall be our legacy?

What will our children say?

Let me know in my heart

When my days are through

America, America I gave my best to you.