As they neared the turn of the millennium, and steeled themselves for the Y2K bug, Americans faced a critical question: Whom would they crown the teen queen of pop?

In 1999 there were four candidates. Britney Spears was an early front-runner, riding the breakout success of “… Baby One More Time.” Christina Aguilera, her fellow former Mouseketeer, was cast as Ms. Spears’s direct opponent. Jessica Simpson entered the field as a quieter, more chaste presence. And then there was Mandy Moore.

“Oh, I knew I was in a distant fourth if there were rankings,” she said earlier this month over tea at the Pierre Hotel in Manhattan.

Two decades later, Ms. Moore is more of a household name than ever. “This Is Us,” the TV show she stars in, is one of the most popular dramas on NBC. Ms. Moore’s character helps tie together the show’s decade-crossing plot points, often in old-age makeup.

“Mandy really centers the entire show,” said Dan Fogelman, its creator. “Rebecca is the only character who exists in all the main story lines, in every time period.”

“This Is Us” has earned her Golden Globe and Emmy nominations, as well as two Screen Actors Guild awards and a star on the Hollywood Walk of Fame. “It kind of changed everything,” Ms. Moore, 35, said.

It also arrived at the tail end of a relationship that had stifled her creativity and warped her sense of self. But she’s past that now, and ready to share new music. “Silver Landings,” her first album in more than a decade, comes out March 6.

“I’m a firm believer in things happening for a reason, and it took the last 10 years of my life to get to this point.” she said. “I really feel like it was worth it.”

Silence and Speaking Out

Ms. Moore’s first album, “So Real,” was a modest success when it was released in 1999: It spent 23 weeks on the Billboard 200 chart, peaking at No. 31 and selling 950,000 copies.

In the years that followed, she leaned into a crossover career, appearing alongside Anne Hathaway in the “The Princess Diaries” and starring with Shane West in the film adaptation of “A Walk to Remember.” As she racked up acting credits, some of which included vocal solos, she continued to record music. None of the albums surpassed her first in sales. Then, after her sixth, she went silent.

That last album, the folk- and country-inspired “Amanda Leigh,” came out in 2009 — also the year she married the musician Ryan Adams. Throughout their relationship, Ms. Moore wrote songs, some with Mr. Adams, for a seventh studio album. Every so often she would share updates with her fans on social media. But nothing was ever released.

“I was so ready. I was so hungry,” Ms. Moore said. At the time, she had no formal representation; she had parted ways with her music manager. Mr. Adams, a prolific solo artist, writer and producer, discouraged her from working with anyone but him on the new album, she said.

As the years went by, Mr. Adams continued to release his own work, and Ms. Moore’s career as a musician stagnated. She began to question her self-worth: “‘Am I good enough? What do I bring to the table?’ Because if my creative partner and romantic partner can’t even make time or doesn’t want to work with me, where does that leave me?”

She and Mr. Adams divorced in 2016, but it would be years until she went public about his treatment of her. And she certainly wouldn’t write about him.

“I’m so done with that person having taken so much of my life and my time,” she said.

Last February, Ms. Moore opened up about her relationship with Mr. Adams in a New York Times investigation of sexual misconduct and emotional abuse allegations against the musician. (Through his lawyer, Mr. Adams denied many of the allegations. After the article’s publication he posted a series of apologies on Twitter “to anyone I have ever hurt, however unintentionally.”)

“I was blown out of the water by the information, some of which was in the article and some of which after the fact I found out wasn’t a part of it,” Ms. Moore said, wiping tears from her eyes.

For months after the article’s publication, people reached out to Ms. Moore — some with their own stories about Mr. Adams and others who had experienced similar treatment in their personal lives. “Women were, are, so hungry to have this conversation, I think, when it involves emotional and psychological abuse,” she said.

She is proud to have spoken up about her experience. Still, Ms. Moore is reluctant to frame Mr. Adams as the center of — or even a turning point in — her story.

“I just don’t want this thing to be about him,” she said, referring to the interview and the article that would come of it. “He’s taken so much for so long from so many people. I can promise you he gets satisfaction being talked about in any capacity. I just know that about him. I haven’t spoken to him in, I don’t know, two years or something, but just knowing him as well as I know him, he really gets off on being talked about.”

The New Album

Over the course of Ms. Moore’s first decade in music, her sound evolved considerably. After two straightforward pop albums, her self-titled third veered clubby and dance-pop, with some Middle Eastern and hip-hop influences. “Coverage,” in 2003, included covers of Elton John and John Hiatt. “Wild Hope” and “Amanda Leigh,” released in 2007 and 2009, were a definitive shift to folk pop.

In November 2018, she married Taylor Goldsmith, the frontman of Dawes, a California rock band. “Taylor is the most profoundly good person I’ve ever met in my life,” Ms. Moore said. Being with him helped encourage her return to songwriting. “There wasn’t a question that if I ever made music again it would be with him,” she said.

“Silver Landings,” the album they wrote and recorded together, is largely forward looking, showcasing Ms. Moore’s growth as a folk musician and an honest, empowering portrait of an artist accepting her past.

The album also touches on her insecurities with returning to music. On “When I Wasn’t Watching,” she addresses this head-on: “My favorite version of me disappeared through longer days and shorter years.” She also confronts herself on “Forgiveness,” singing, “I wanted to be good enough for you until I wasn’t good enough for me.”

She and Mr. Goldsmith brought in Mike Viola, a songwriter and producer. “She really knew what she wanted to sing about and didn’t know how, and that’s what we spent most of the time working on,” Mr. Viola said. “Not what she wants to say, but how do we craft this in a way that makes her feel the most authentic and true to her core?”

For the album, Ms. Moore leaned on the influence of artists who have always inspired her: Joni Mitchell, Jackson Browne, Warren Zevon. She has spoken publicly about being embarrassed by the music she made at the beginning of her career because of what little creative control she had.

Now she doesn’t “begrudge it in the same way” she once did, she said. She even pays tribute to her teen pop days for the first time on “Silver Landings” with the nostalgic single “Fifteen.”

“I think I’ve really turned a corner on the idea of having a lot of affection for that part of me and how that 15-year-old was able to navigate what could have been a very tricky world,” Ms. Moore said. “That I’m still here is proof that I did something right, I guess.”

Campaign Stops and Tour Dates

Over the years, Ms. Moore’s fan base has come to encompass five generations: the millennials and Gen Xers who remember her ’90s pop stardom, and the wide-ranging audience (from the silent generation to Gen Z) of the family-friendly “This Is Us.”

“Social media obviously changed the ability to connect one on one with folks and shape our own narrative,” Ms. Moore said. “I think young women who were fans as teenagers have grown up with me, maybe, and now their moms, aunts or grandmas even are familiar with my work through ‘This Is Us.’”

Now, that she has their attention, Ms. Moore is hoping to direct it toward a Democratic presidential primary candidate: She is a surrogate for Pete Buttigieg’s campaign.

Mr. Buttigieg, who is second behind Senator Bernie Sanders in the delegate race, has attracted many celebrity donors, including Sharon Stone, Anna Wintour, David Geffen, Tom Ford, Gwyneth Paltrow and Ellen DeGeneres.

“I think he’s the most qualified, and he’s the most electable,” Ms. Moore said, though she added that she would support whomever wins the Democratic nomination.

Ms. Moore has campaigned for Mr. Buttigieg in Florida, Iowa and Louisiana, and has posted about him on her social media accounts. According to filings with the Federal Election Commission, she has donated more than $3,800 to his campaign, about $1,000 of which has been earmarked for the general election to comply with contribution limits.

Chris Meagher, the national press secretary for the Buttigieg campaign, described Ms. Moore as a “kind, hopeful person who saw Pete’s message of unity and bringing people together and I think that she wanted to share that with folks.”

While she had been personally politically active, she had never endorsed a candidate during the primary before. “If I can do anything and use my platform to, you know, help garner support for something and someone that I really believe in then I’m all for it,” she said.

As Mr. Buttigieg continues his tour of the nation, Ms. Moore will be hitting the road, too, promoting “Silver Landings.” She also plans to start writing her next album in the coming months and to record it over the summer. It took too long, she said, for this one to arrive; she won’t let that happen again.

“I’m not going to have this 10-year respite between being creative,” she said.