Seol Yoon-a was born on January 26, 2004 in Daejeon, South Korea.1 From an early age, she demonstrated both academic excellence and leadership qualities, serving as student council president in elementary school and class president during her high school years.2 She began training in ballet and modern dance as a toddler, establishing the foundation for her performance abilities that would later define her career.2

Despite her young age, Sullyoon passed auditions for multiple major entertainment companies, including JYP, YG, SM, The Black Label, and Fantagio.2 When asked about her decision, she revealed that she ultimately chose JYP Entertainment because of her admiration for TWICE, the company's most successful girl group at the time.2 Her audition repertoire included MOMOLAND's "Wonderful Love," Taeyeon's "11:11," and Ailee's "Singing Got Better," showcasing her vocal versatility and range.2 She signed with JYP Entertainment in 2020 and trained for approximately one year—one of the shortest training periods among JYP artists—before being selected for the company's new girl group.

On September 2, 2021, Sullyoon was revealed as the fourth member of JYP's upcoming girl group through a performance cover of Sunmi's "Full Moon."3 The reveal immediately garnered attention, with her "Full Moon" qualifying video quickly accumulating over one million views on NMIXX's YouTube channel, becoming the third video on the channel to reach this milestone.3 Even before the group's official debut, online discussions highlighted her striking visuals, with many fans and netizens noting her potential to become one of fourth-generation K-pop's defining visuals.

NMIXX officially debuted on February 22, 2022 with the single album "AD MARE."4 Netizens were looking forward to NMIXX's performances and to enjoy their debut track "O.O."4 She also mentioned her commitment to learning multiple languages to better communicate with international audiences, expressing hopes to perform abroad once the pandemic situation improved.4

Throughout NMIXX's releases, Sullyoon has consistently contributed to explaining the group's artistic vision. During the press conference for their first EP "expérgo" in March 2023, she described how the album connected to their previous work: "The storyline of this album is a sequel to our previous album as we tried to connect the dots to portray our worldview."5 "Love Me Like This" music video drew inspiration from "The Wizard of Oz," with characters like the Lion finding courage, the Tin Man finding love, and the Scarecrow finding wisdom.5

For the summer 2023 single album "A Midsummer NMIXX's Dream," Sullyoon explained the concept at a press conference: "The storyline from our first mini album 'expergo' continues into this new album in which we finally meet with Nswers (the group's official fandom) at a party and enjoy a dreamy summer night together."6 Her ability to articulate the group's artistic direction demonstrated not just her role as a performer but as someone deeply engaged with NMIXX's creative narrative.

In a 2025 interview with Elle Korea while preparing for the "Fe3O4: FORWARD" album, Sullyoon reflected on the group's evolution: "I would say it's our comeback. The members and I have been discussing how we can showcase our performances and songs even better. Our title track, 'KNOW ABOUT ME,' stays true to NMIXX's signature style but has a more understated feel compared to our previous title tracks. I believe it will highlight a more mature side of us."7 The Korea Herald also quoted her saying, "We would like to show a more mature and different sides of us," demonstrating her awareness of the group's artistic growth trajectory.8

On March 23, 2023, it was announced that Sullyoon would join MBC's "Show! Music Core" as a special MC, filling the position left by former IZ*ONE member Kim Min Ju.9 She would be joining NCT's Jungwoo and Stary Kids' Lee Know as the program's MC trio. After a successful trial run, Sullyoon was officially confirmed as a permanent MC on April 6, 2023, with her tenure beginning on April 15, 2023.10

Upon her confirmation, Sullyoon expressed her feelings: "I'm so happy and honored to be able to stand as the MC of Music Core, which was played by great seniors. It's my first challenge, but I'll show you a new and diverse side of me every week, so please look forward to MC Sullyoon a lot."11 In November 2023, THE BOYZ's Younghoon and actor Lee Jung Ha joined her, forming a new MC trio that would host the show together until early 2025.12

Soompi reported that on February 8, 2025, it was confirmed that Sullyoon, Younghoon, and Lee Jung Ha would be stepping down from their MC positions, with their final episode airing on February 15, 2025.13 Sullyoon's tenure lasted approximately one year and 10 months, during which she became known for her warm hosting style and natural chemistry with her co-hosts.13 In her Elle Korea interview, she expressed enthusiasm about music show appearances: "We usually promote on music shows for about three to four weeks. Many people think appearing on music shows is challenging due to the long recording sessions and wait times, but there are also many fun aspects."7

Sullyoon's visual appeal has consistently garnered recognition throughout her career. On October 16, 2025, she attended the 20th W Korea Breast Cancer Awareness Campaign Charity Event at the Four Seasons Hotel Seoul alongside IVE's Jang Won-young and Aespa's Karina.14 The publication noted that during the photo session, "Sullyoon completed the trio with a refreshing, pure charm that fans often describe as 'the textbook definition of innocence,'" while photos of the three idols together quickly went viral online with fans calling it "the ultimate K-pop visual lineup."14

Her visual reputation has been consistent since pre-debut, with many considering her one of fourth-generation K-pop's standout visuals. This recognition, combined with her solid vocal abilities and dance skills, has established her as a well-rounded performer who embodies NMIXX's "all-ace" concept where every member excels across multiple disciplines.

In her Elle Korea interview, Sullyoon discussed her nickname "General," stating: "I really like that nickname. I hope the other NMIXX members and the people around me see me as someone they can rely on, just like a real general."7 She emphasized the importance of her bond with her fellow members: "For me, the most reliable presence is my fellow members. Whether we're on stage or traveling overseas, as long as we're together, I feel confident."7

Despite her strong stage presence and leadership qualities, Sullyoon has described herself as initially shy when meeting new people, though she becomes more playful and comfortable once she grows close to someone.15 Her hobbies include spending time alone, walking in the rain, baking, and collecting snacks and writing in her diary.15 Among NMIXX members, she's nicknamed "Snorlax" for sleeping the longest, reflecting a quieter, more introverted side that contrasts with her professional persona.15