She took on her first leading role in teen drama Ma Boy (2012) and since then has starred in many TV series including high-school drama Who Are You: School 2015 (2015), horror comedy Hey Ghost, Let's Fight (2016), historical melodrama The Emperor: Owner of the Mask (2017), romantic comedies Radio Romance (2018) and The Tale of Nokdu (2019), teen suspense romance Love Alarm (2019–2021) and Korean folklore River Where the Moon Rises as an assassin.

[12] At the age of 21, Kim became the youngest South Korean actress to have more than 10 million followers on social media, alongside actor Lee Min-ho.

[20] In 2016, according to Singapore's national newspaper The Straits Times, Kim revealed in an email interview with the paper why she chose homeschooling instead of enrolling in high school.

[21] Kim debuted as a child actress in 2006, playing a supporting role in the Drama City special "Ten Minute Minor".

Kim was confirmed to make her big-screen debut in Man of Vendetta (2010) as Joo Hye-rin, a daughter of a well-respected pastor who gets kidnapped.

[24] She continued to portray the child counterparts of the female protagonists in television series such as The Thorn Birds (2011), The Duo (2011) and Sin of a Family (2011).

[38] Kim reunited with co-stars from Rooftop Prince (Park Yoo-chun) and Moon Embracing the Sun (Yeo Jin-goo) respectively, in a melodrama Missing You.

[42][43] She played the role of Lee Soo-yeon, bullied by her schoolmates and called "the daughter of the murderer", who gets kidnapped and sexually assaulted while trying to save her friend.

[46] In 2013, Kim made a surprise appearance on Iris II: New Generation as the childhood counterpart of the female protagonist[47] and starred in The Secret of Birth as a girl with a genius-level brain.

[51] The three received much attention because of the combination of singers, actors, and broadcasters even though they initially showed a bit of immature progress, but amplified expectations of how they expressed their charms despite having different careers.

[57][58] In 2015, Kim made a special appearance as the sister of the male lead in A Girl Who Sees Smells,[59] played by Park Yoo-chun, whom she reunited with for the third time after Rooftop Prince and Missing You.

[65][66] Kim then starred in a mystery-school web drama Nightmare Teacher alongside Lee Min-hyuk, playing a class president who discovers mysterious secrets of the school.

[69] The same year, Kim starred in Park Hye-ryun's three-episode drama special Page Turner opposite actors Ji Soo and Shin Jae-ha.

[75] She made her next acting move in the horror-comedy Hey Ghost, Let's Fight with Ok Taec-yeon,[76] and played as the 13-year-old Princess Deokhye in the film The Last Princess,[77] for which Park A-reum of K-pop Herald praised Kim for her in-depth emotional acting in the scene before her farewell to her mother (which Park called heartbreaking), as well as the high sync rate with Son Ye-jin.

[78] Also, Jung An-ji of Sports Chosun praised her for the historical accuracy of portraying the princess: citing she acted "perfectly" with the life of a girl during the Korean Empire.

[86] Despite its high ratings,[87] the time of the drama's original run coincided with her slump period — Kim expressed how she made efforts to understand her character as a heroine.

[89] She made a special appearance in drama While You Were Sleeping to show her support for scriptwriter Park Hae-ryun, who she worked with on KBS's Page Turner.

During the press conference for the premiere of Radio Romance held on 25 January, the PD addressed online criticism regarding the outdoor water filming, despite the weather warnings.

[102] Kim received positive feedback from viewers of the premiere for her strengths as a host, as noted by Korea Economic TV — audience engagement, her "steady" voice, charisma, as well as her styling, which the publication deemed "colorful".

[112] The same year, she was cast alongside Jang Dong-yoon in a romantic comedy drama set in the Joseon period, The Tale of Nokdu as a clumsy and hot-tempered Kisaeng trainee.

"[116] The pair were donned the nickname "Manhwa tearing" chemistry by the viewers for capturing everything from laughter to excitement and adding their colours to the original characters.

On 1 October, an official statement from Kakao M revealed that Kim received 815 shares (about 100 million won) of it to resolve issue rights to strengthen solidarity with affiliates and entertainers.

[127] The drama was caught in a controversy following bullying accusations made against Ji Soo, who played the show's male protagonist.

[138] In July 2023, she returned to the small screen with the tvN romantic comedy series My Lovely Liar,[139] in which her performance and chemistry with Hwang Min-hyun was acclaimed by Joan McDonald of Forbes as appealing.

[148] On 25 February 2020, Kim donated ₩10 million through Hope Bridge Association of the National Disaster Relief to prevent the spreading of the COVID-19 pandemic in South Korea.

[153] She became the face of Nintendo 3DS real-time pet simulation video game, Nintendogs + Cats with Kim Yoo-jung,[154] Yuhan-Kimberly's "Teen's Nature" brand,[155] Union Bay with Park Seo-joon and Lee Hyun-woo,[156] and Nongshim's Shin Ramyun with Yoon Doo-joon.

[173] The same year, G-Market announced Kim as their model for the launch of Korea's first integrated brand lift package through cable channels and online.

[178] Kim's image was the main contributor that leads a successful product to sell 700,000 quantities in two months, sold out "Ink Airy Velvet No.

[216] In particular, the charm of Kim's tone shines in the drama from a plump romantic comedy to a complex, subtle feeling of conflict between the family's revenge and the love she felt for the first time in her life.

[234] Following the release of hit dramas Love Alarm and The Tale of Nokdu, the press gave Kim "Come-out-of-manhwa girl" (만찢녀 (만화 찢고 나온 여자)) due to the perfect sync rate with the original characters and emotional performance.