Kim So-hyun was born in Australia. She moved to South Korea in 2003 when she was four years old. She has a younger brother. Her father died when she was 9 years old.

Kim debuted as a child actress playing a supporting role in the 2006 Drama City special titled Ten Minute Minor. Then, she is diligently increasing her appearances from A Happy Woman (2007), Que Sera Sera (2007), Hometown of Legends (2008), My Name Is Pity (2008), Wife and Woman (2009) and Ja Myung Go (2009).

Later, she signed a management contract with Sidus HQ in 2010. Then, she was casted in Becoming a Billionaire (2010) and King of Baking, Kim Takgu (2010). 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. Kim was cast through a fierce competition of 500:1 which she was able to convey expressions without words through her modest facial expressions, which are hard to see for child actors. 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). She then starred in a family comedy film, Spy Papa about parents and children’s relationship during inter-Korean relations in 1974.

Kim transferred from Hoe-ryong Elementary School in Gyeonggi-do to Towol Elementary School and graduated in February 2012. Then, she graduated from Yongin Munjung Middle School in 2015. She was homeschooled for her secondary education, and passed the high school graduation exam in 2017. The same year, she enrolled at Hanyang University’s Department of Theater, through rolling admission. Kim attended the 79th entrance ceremony held at Hanyang University in Seongdong-gu, Seoul on February 28, 2018.

In 2012, Kim appeared in six works in the first half of this year. She starred in a romanctic fantasy television series, Padam Padam and a historical comedy film, I Am the King. She gained public attention when she featured in the fantasy-period drama Moon Embracing the Sun as the younger version of the second female lead. Kim received commend from the audience and the director of how well she portrayed the antagonist’s desire realistically. The drama managed to rank number one in its time slot throughout its run and achieved a peak recorded viewer rating of 42.2 percent thereby earning the “national drama” status. Kim became “Korea’s little sister” at the same time. This was followed by fantasy-comedy, Rooftop Prince as an evil sister, Love Again and a high school student whose roommate is a female idol star in Ma Boy.

In 2013, Kim made a surprise appearance on Iris II: New Generation as the childhood counterpart of the female protagonist and starred in The Secret of Birth as a girl with a genius brain. Then, she played the younger version of Lee Bo-young’s character in the popular Korean drama I Can Hear Your Voice. On June 20, Kim co-host MBC’s music program Music Core along with Minho of SHINee and Noh Hong-chul. The three received a lot of attention because of the amazing combination of singers, actors, and broadcasters eventhough they showed a bit of immature progress from the beginning but amplified the expectation of how they expressed their charms despite having different career groups. She then got cast in The Suspicious Housekeeper, a Korean remake Japanese hit drama, Kaseifu no Mita. In the same year, Kim was reported along with Kim Yoo Jung and Yeo Jin Goo as the top 3 child actors who do earn above average salary for child actors. It was reported that Kim received 4-6 million won per episode.

In an interview in 2013, she revealed she was never been formally trained for acting in the past. While filming for Pure Love, she lived in Goheung. Kim said that, when there was no filming, she went around Goheung city alone and listened to the stories of the residents. She explained she looked around every corner of the village for how she could be part of it.

In 2014, Kim has been cast as a child actress of Oh Yeon-soo in MBC drama, Triangle. Kim challenged her first dual role and first genre through OCN’s new drama Reset. Later, she was cast in KBS2 special drama, We All Cry Differently which won the 2013 KBS Screenplay Contest.

In 2014, Kim joined in the “HAPPY Together Briquette Donation Campaign” to donate 1 million briquette for the elderly, disabled families and low income families for heating during cold season.

In 2015, Kim did a special appearance as the sister of the male lead in A Girl Who Sees Smells. In the drama, she reunites with Park Yoo-chun for the third time after Rooftop Prince and Missing You. On April 18, Kim steps down from her Music Core MC posts after two years. Kim starred in KBS’s school series Who Are You: School 2015, playing dual roles as twins Lee Eun-bi and Go Eun-byul. She was awarded “Star of the Year” at the 8th Korea Drama Awards for her performance. On November 21, Kim held her first overseas promotion schedule at Sunshine City, Hong Kong. At the end of the year, Kim became the MC of the 2015 KBS Drama Awards with Jun Hyun-moo and Park Bo-gum.

In 2015, Kim has become one of the most in-demand endorsers after her hit drama Who Are You: School 2015. She was chosen to become the face of a women’s clothing brand, Soup because of her “girl’s liveliness and a romantic lady’s vibe”. Kim was selected as the 25th Pocari Girl for Pocari Sweat due to her “pure innocence and cheerful image”. A photograph went viral on social media after Kim retweeted and left a comment, “Graduation (Graduation Photo) ㅋㅋㅋ” of a Uijeongbu High School male-student who recreates Kim’s signature drinking pose, wearing short shorts and almost lying on the floor for his graduation photo. In response, Dong-A Otsuka gifted the student several Pokari Sweats, Oronamin C and named him the “Pocari Man”. In 2015–16, she was featured in Domino’s Pizza’s advertisement with Kim Woo-bin. Two of Kim So-hyun’s costume in Domino’s Pizza advertisement went on for an online-auction and the donating proceeds to the Green Umbrella Children’s Foundation. She also appeared in commercials for POST Honey Oz cereal, and Korea’s school uniform Elite. Kim became the longest Elite endorsement model from 2014 until 2016. She has worked alongside Winner, Shin Ae-ra, and BtoB.

In 2016, according to The Straits Times (a daily English language newspaper in Singapore), Kim So-hyun revealed in an email-interview with the paper why she chose homeschooling instead of enrolling in high school; she said that while managing her acting career, she barely had time to study during her mid-school days (which made her having to take her exams unprepared) and missed out activities with her classmates, and this similarly occurred in her elementary school days. Kim chose homeschooling for her high school education because she did not want to give up her education and career, and with this decision, Kim felt it would allow her to dedicate more time in both filming and studying.

In 2016, she returned to the big screen in a romance film, Pure Love opposite Do Kyung-soo, playing the heroine of the film who has a beautiful voice but suffers from a leg injury. Kim then starred in a mystery-school web drama Nightmare Teacher alongside Lee Min-hyuk, playing a class president that discovers mysterious secrets of the school. The drama was filmed and featured nine students from Hosan University. The same year, Kim starred in Park Hye-ryun’s three-episode drama special, Page Turner opposite actors Ji Soo and Shin Jae-ha. She played the role of a “piano genius” who lost her sight after an accident. The drama achieved 600,000 views and recorded an unusual number as a one-act play. Kim’s first fan meeting Lovely Day in Taiwan was held at Ming Chuan University on April 9. She was dubbed as the “Korean Wave Fairy” by the Taiwanese media. On June 4, Kim hosted the 2016 Dream Concert with Leeteuk and Hong Jong-Hyun. She then starred in the horror-comedy Hey Ghost, Let’s Fight with Ok Taec-yeon, and played as the 13 years old Princess Deokhye in the film The Last Princess, for which she was praised by critics and audience for her in-depth emotional acting in the heartbreaking scene before her farewell to her mother, as well as high synchronize rate with Son Ye-jin. Additionally, she was also praised for not only showing the noble and upright character that she should have as the last princess of the Korean Empire but also acted perfectly with the life of a girl during the Korean Empire. She had a recurring guest role in the hit fantasy drama Guardian: The Lonely and Great God. Kim showed an overwhelming presence and increase audience immersion in the early stage of the drama making a big impact as a cameo.

On April 16, 2016, Kim So-hyun has been selected for two consecutive years as a 2016 Pocari Sweat advertising model to commemorate the brand’s 30th anniversary. It is the first time in 15 years since Son Ye-jin in 2001. The same year, G-Market announced Kim So-hyun as their model for the launch of Korea’s first integrated brand lift package through cable channels and online.

In 2017, So-hyun participated in Korean dubbing for the character “Mitsuha Miyamizu” in the international hit Japanese animated drama film Your Name. Kim then starred in the historical and political drama The Emperor: Owner of the Mask alongside Yoo Seung-ho which premiered on May 10. This marked her first adult historical drama after five years since Moon Embracing the Sun. Despite of its high ratings, the drama eventually became her slump period. Kim expressed how she made efforts to understand her character as a heroine. She felt lost and started losing confidence in herself as an actress. As everybody was praising her acting and visual, she felt embarrassed because she could not come to a full understanding of who her character was.

Kim held her first domestic fan meeting “Lovely Day” on June 3. 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. In August 2017, she ended her contract with her agency Sidus HQ, after seven years in the company. On November 11, Kim So-hyun completed her second Taiwan fan meeting Sweet Dream with Allets. In December, Kim launched her one-person agency, E&T Story Entertainment, in partnership with LOEN Entertainment. The agency is currently led by Park Chan-woo, Kim’s manager in her SidusHQ days.

In 2017, Kim So Hyun and Ji Chang-wook donated their dubbing fees for Your Name to the Korea Barrier-Free Film Commission.

In 2018, Kim starred in romance drama Radio Romance alongside Yoon Doo-joon, which began airing on January 29. She plays a radio scriptwriter who isn’t exactly talented in writing. On January 24, a photo was shared on the online community saying that Kim was shooting underwater. The photo shows a woman wearing a hanbok in the water on January 21. On this day, the lowest temperature was recorded below minus 16 degrees. During the press conference for the premiere of Radio Romance held on January 25, the drama’s PD addressed online criticism regarding the outdoor water filming, despite the weather warnings. He issued an apology stating that “Kim So Hyun’s outdoor water filming wrapped up on Sunday (Jan 21st). We debated on it a lot, since she would be getting in the water. We ensured safety equipment nearby, as well as a camping car on set, and finished filming in the shortest amount of time possible. Due to time constraints, an action stunt double filmed additional outdoor water scenes yesterday (Jan 24th). It was filmed by an action actor, not Kim So-hyun, wearing a winter suit and shot in a similar situation (Jan 21st). The number of shots was done with one take and protection was taken right away. We apologize for causing concerns with this matter. The filming set is our lives. Naturally, safety is important.” At the press conference, Kim’s hand was visually seen red.

In January 2018, the Pyeongchang Organizing Committee for the 2018 Olympic & Paralympic Winter Games (POCOG) chose Kim and Yoo Seong-min as the National Representative of Honorary Smile to represent Korea’s smile and kindness.

On April 21, 2018, Kim participated in “S.E.S 10th Green Heart Bazaar” held by the first generation K-pop girl group, S.E.S. Kim and many other celebrities gave generous good deeds by selling items at the bazaar. The proceeds that were collected are donated to the Green Umbrella Children’s Foundation and KARA.

In early 2019, Kim So-hyun was selected for two consecutive years as the MCs for 28th Seoul Music Awards alongside Kim Heechul and Shin Dong-yup. She held her second fan meeting in Korea, Sso.Affirmation.Happiness: Kim So Hyun’s Little & Indeed Happiness ahead of her birthday with an attendance of 300 people. On June 29, she also held her first-anniversary fan meeting in Tokyo, Japan. Kim starred in Netflix’s original production Love Alarm, based on the popular webtoon of the same name. Kim explained her character is experiencing the emotion of love for the first time, and it reminded of herself. She decided to tap into those feelings as she wanted to portray a living and breathing character with Jo-jo. She was highly praised for showing off her original character, high synchronize rate and rich and stable acting performance in the series. Forbes’s Joan MacDonald citing that Kim fits well with the character Jojo. Further, the Netflix series was a commercial success as it ranked as one of the platform’s top shows during 2019.

The same year, she was cast alongside Jang Dong-yoon in a romantic comedy drama set in the Joseon dynasty, The Tale of Nokdu as a clumsy and hot-tempered Kisaeng trainee. Chon Kye-young and Hye Jin-yang, the author of both webtoons named Kim as their first choice in casting the leading woman. Kim So-hyun’s character was able to mesmerize the viewers because Kim blended so well with her character. Jang Dong-yoon stated, “I was convinced that there would be no better actress to play Dong Joo other than So Hyun, I was very grateful to have met my best partner in her.” 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. Her role as Dong Joo earned her the Excellence Award at the year end KBS Drama Awards. The series was another success for Kim by becoming one of the top 10 out of 104 most talked primetime Korean dramas aired in 2019.

On April 5, 2019, Kim So-hyun donated ₩10million to help support the victims of Sokcho Fire. Kim also donated ₩10million with her fans to Ajou University Hospital Trauma Center. This is the result of the fans giving support towards Kim’s idea who wanted to achieve and sharing on her June 4 birthday. Her fans also donated 61 blood donation certificate to the hospital along with the fund to help patients who were living with difficulties. On December 13, she donated 100kg of rice to the social welfare corporation network for underprivileged and undernourished children in the future.

In 2019, Kim expressed that she has no role models. She commented, “I don’t even know myself. I think it’s time to get to know myself more than the role model. If I find myself, I can find my role model then.”

In 2015–17, Kim was appointed as the face for young girls’ makeup brand Peripera. In three days, Peripera “Ink Airy Velvet” has sold 30,000 quantities. Kim So-hyun’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. 2” and “Ink Color Cara” winning in the Glow Peak Beauty Awards mascara category. In August 2019, Korean media reported Soup to become Korea’s first young casual brand to record ₩100 billion sales in Korea after commissioning Kim as their promotional model for 2019 Fall/Winter Collection.

In 2020, Kim’s travel reality show Because This Is My First Twenty surpassed 6 million views as of May 2020 on YouTube, Naver TV and Facebook. On October 5, Kim confirmed her role as the protagonists in The Moon Rising River. She plays as a female general, who was born as a princess but raised as a general, and chases for her goal to straighten the ruined statue of her country, Goguryeo.

On February 25, 2020, Kim donated 10 million won through Hope Bridge Association of the National Disaster Relief to prevent the spreading of the COVID-19 pandemic in South Korea. According to the organization, the donation was to help the vulnerable people and purchasing health and hand sanitizers to prevent the spread of the disease. On August 5, Kim donated 20 million won to help flood victims who suffered from the heavy rain. In October, Kim participated in the “MANNA Charity Bazaar” to support the treatment costs of children suffering from rare diseases. A representative official said, “People who have been consistently sponsoring and volunteering have been together under the name of Manna.”.

Kim So-hyun continued endorsing various products that ranged from food to clothing and cosmetics such as, Norwegian fashion shoes brand Skono, chicken brand Pelicana Chicken, Samsung Securities, naturalism-oriented cosmetics Hanyul, colour contact lenses Bausch & Lomb’s Lacelle, and continued to be Soup’s representative and model since 2015. In April 2020, Samsung Electronics introduced Bixby Celebrity Voice, an artificial intelligence (AI) voice assistant with Kim as their AI speakers. Kim’s Celeb Alarm gained popularity in South Korea and overseas, and topped Popular Download Ranking.