Jang spent most of her childhood in her birthplace, Yeokchon-dong Eunpyeong District in Seoul, South Korea. She appeared with her father, Ju Heo-seong who is also an actor, in a play Les Misérables, in her primary school days, thus sparking her interest to become an actress. Jang also went on to become an advertisement model for some television advertisements in her high school days before entering into the Department of Theater, the Faculty of Fine Arts major in Acting at Chung-Ang University in March 2000. Furthermore, she participated in band, performed instruments in musicals and acted in many plays. She then graduated 10 years after on February 19, 2010. The delay is due to her continuous work since her debut after she entered the University. She also received an alumni association award for her contributions to the University during the graduation rites.
Jang made her debut in the entertainment world as a singer on May 2001. She started her singing career by becoming a trainee and signing a contract with SM Entertainment. However, SM Entertainment dropped her due to assumptions that she would have lesser or no popularity than the other competing artists.
Jang released her debut album First Story with the title track Burying My Face In Tears. Initially, it was not well received and only reached number 12 in Korean music charts. After starring in the popular sitcom New Nonstop, she became more well known and released the other tracks in the album such as her pop ballad style song, Confession and the April Story, ranked at the top in various music charts. The album sold 300,000 copies. Jang then became a host for MBC's music show, Music Camp and KBS's talk show Love Story. By the end of 2001, she received several New Female Artist awards from year-end Music Awards ceremonies and New MC awards from Entertainment Awards ceremonies.
In October 2002, Jang released her second album Jjang Nara Vol.2 Sweet Dream. The song Sweet Dream became immensely popular and reached number 1 in Korean music charts, instantly making Jang a household name. The album also became one of the top selling albums of that year in South Korea. Due to the success of Sweet Dream, Jang won several awards including two Daesang awards or the Grand Prize (equivalent to Korean Top Artist of the Year) from MBC Music Festival and KBS Music Awards. She also received the Korean Singer of the Year from China's CCTV-MTV Awards in 2003.
In December 2003, Jang released her third album aptly titled 3rd Story. The album was also popular and produced hit songs that went to number 1 but it did not surpassed nor equaled the success of her second album.
Jang released a Best Hits Album in 2004 consisting of songs from her 3 previous albums. She followed it up with her 4th album titled My Story released in December 2004, consisting of hit songs such as "I Love School" and "Winter Diary".
With her popularity in China, she also made a career in music overseas by releasing Chinese-language albums. Her first Chinese album was a huge success, making her the first foreign artist in China with over 1 million copies sold. This was followed by the release of two more Chinese albums, Kungfu (2005) and Flying High (2006).
She returned to the Korean music scene in 2007 with her fifth Korean album entitled She, which consists of medium tempo “Masquerade” and the dance piece “You & I”. The following year, she released a multi-lingual album titled Dream of Asia, which includes 26 songs in 5 languages, including Mandarin, Cantonese, Korean, Japanese and English. Jang held a mini concert in Beijing to promote the album. During the 2008 Beijing Summer Olympics, Jang was the only singer from a non-Chinese-speaking country to appear in the 2008 Olympic song Beijing Welcomes You.
In 2009, she released a duet with Jimmy Lin for the soundtrack of their film Flying With You. The track was produced by famed Singaporean musician JJ Lin.
In 2012, four years after releasing Dream of Asia, Jang returned to the Korean music scene with the digital single I Only Think Of You. The same year, she released her fourth Chinese album Love Journey.
In 2013, she recorded a TV campaign song named “Nanoom Song” as the new face of the Community Chest of Korea.
Jang also has a successful acting career. She first appeared in the popular MBC TV sitcom New Nonstop, and received attention for her cute image.
In 2002, Jang landed her first leading role in a drama in SBS's romantic comedy Successful Story of a Bright Girl. The drama is well received and recorded high audience ratings. She won the Best New TV Actress Award at the 2003 Baeksang Arts Awards. The success of the drama and her hit song "Sweet Dream" launched her to stardom in South Korea that year. The same year, she starred in another romantic comedy series My Love Patzzi which also attained high ratings.
In 2003, she made her feature film debut in the film Oh! Happy Day.
In 2004, she came back to the small screen and starred in MBC's weekend drama Love Is All Around, followed by KBS' romance drama Wedding. Wedding established Jang as an actress, and she received viewer acclaim for her portrayal of awoman’s growth and identity in marriage.
In 2005, with her increasing popularity in China, she made a bold move by moving to China to start her singing and acting career. Her first mainstream Chinese drama is Bratty Princess. The success of Bratty Princess catapulted her as a hallyu or Korean Wave star in China. She made several other drama series in China which includes Good Morning Shanghai in 2007, Iron Masked Singer in 2010, and Unruly Qiao in 2011.
In 2009, she returned to the big screen with Sky and Ocean, playing a gifted violinist with a mental age of 6 years old, diagnosed with Savant syndrome. The movie was a commercial failure, and was criticized for Jang's unfair nomination at the Grand Bell Awards even before the movie was released. However despite the controversy, Jang won the Best Actress for a Foreign Film Award at the 19th China Golden Rooster and Hundred Flowers Awards. The film also became the first Asian film to be invited to the 8th Tirana International Film Festival in Albania, where it won the Media Award.
In May 2011, Jang starred in KBS romantic-comedy Baby Faced Beauty. This marks her return to Korean screens after six years. The series averaged 10% ratings throughout its run and won favorable reviews. She later won the Excellence Award for an Actress in a mini-series at the 2011 KBS Drama Awards.
The following year, she filmed her first Chinese movie Flying With You, starring opposite Taiwanese singer and actor Jimmy Lin. She also made a cameo appearance in another Chinese film starring Jaycee Chan titled Whoever. The same year, she appeared together with her father in a Chinese drama entitled Race Course.
In December 2012, Jang reunited with her Baby Faced Beauty co-star Choi Daniel for KBS's teen drama School 2013. She received her second consecutive Excellence Award for an Actress in a mini-series at the 2012 KBS Drama Awards.
After filming for School 2013 concluded, Jang immediately returned to China to film a drama titled Red Palaquin.
The year 2014 proved to be a busy year for Jang with three TV projects under MBC network. In July 2014, Jang played the lead role in Fated to Love You, the Korean adaptation of the 2008 Taiwanese hit drama of the same title. This TV series reunited her with Jang Hyuk 12 years after both starred in the highly rated drama Successful Story of a Bright Girl. Fated to Love You was a hit in China and gained 200 million views. Shortly after, Jang starred in a one-episode drama special entitled Old Farewell for MBC's Drama Festival, pairing her once again with Jang Hyuk. She then took on the lead role opposite Shin Ha-kyun in the fantasy-romantic-comedy drama Mr. Back. She later won the 2014 MBC Drama Awards Top Excellence Award Best Actress in a Mini-Series for both TV drama series she starred in that year.
In 2015, Jang played a police detective in the mystery thriller Hello Monster. In 2016, Jang starred in the romantic comedy One More Happy Ending, portraying a former pop idol.
In 2017, Jang was cast in the drama Housewife Detective where she will play the role of a single mother. However due to production issues, filming of Housewife Detective was indefinitely suspended. Later in the year, she was cast in the romantic fantasy drama Confession Couple.
Jang does many charity work such as sending free powdered milk to the hungry North Korean children. She also works with the FHI Charity organization.
In 2004, Jung was named public relations envoy for China by the Embassy in Korea of the People's Republic of China.
In 2007, Jang held a fund-raising concert for child patients of leukemia in China. The Jang Foundation was established from the money raised during Jang's fan club meeting at her June 9 concert in Beijing, which was held to mark the 15th year of diplomatic relations between China and South Korea. Twelve hundred seats at the concert venue sold out early. After the concert on stage, a Chinese charity organization appointed Jang as a goodwill ambassador, making her the first foreigner to receive such an honor. The same year, she was appointed as one of the goodwill ambassadors for the China-ROK Exchange Year.
In the aftermath of the 2008 Sichuan earthquake, Jang donated 150,000 dollars to a charity organization in China and 8 billion won of clothing for the victims.
In June 2010, Jang was appointed as an associate professor at the Beijing Huajia University.
In 2011, Jang was appointed as Seoul’s Gangnam-gu's ambassador to promote tourism in the area.
In 2015, Jang was recognized for her charity activities by the Ministry of Health and Welfare.