Eun-jeong was born in Seoul, South Korea. Her mother, a graduate of Ewha Womans University, is a former piano teacher who works as Eun-jeong's agent. While attending seventh grade, Eun-jeong started taekwondo lessons and won three different competitions. Her mother made the decision to quit teaching and manage Eun-jeong's career upon her high school graduation in 2007. Later that year, Eun-jeong enrolled in Dongguk University, where she took performance courses. She is an only child and has been quoted as explaining, "My mother had me 10 years after she was married to my father, which seems more hurtful. Upon watching several famous performers in the past, she wanted to become an actress. Now that I have, she is very pleased I have acting as a priority. She believes her original prayers were answered."
In 1995, when Eun-jeong was seven years old, she participated in the "Little Miss Korea" pageant and won. That same year, she appeared in the youth drama "신세대 보고서 어른들은 몰라요" ("Sinsedae Bogoseo Eoreundeureun Mollayo", "A New Generation of Adults"), which aired on Korean Broadcasting System. Afterwards, she had several minor roles in movies and Korean dramas, along with being cast in a handful of commercial films.
Eunjung's acting debut was in Hello, My Teacher! where she appeared as a high school student who was unfairly cheated out of a grade which could have put her above the top 40 point. She also appeared in Death Bell alongside Nam Gyuri, Lee Beom-soo and Kim Bum. In the said film, she played the role of Kim Ji-won who was murdered by her own teacher.
She appeared in SG Wannabe's music video "Gasiri" ("가시리") from their 2007 album Story In New York. Later, she would also be seen in FT Island's music videos of "Thunder" ("천둥"), "Only One Person" ("한사람만"), and "A Man's First Love Follow Him To The Grave" ("남자의 첫사랑은 무덤까지 간다").
In July 2010, Eunjung was cast in her first movie role for the thriller White: The Melody of the Curse (화이트: 저주의 멜로디 ). Directed by Kim Gok and Kim Sun, filming began in November 2010. The film was released to South Korean cinemas on June 9, 2011.
T-ara’s agency Core Contents Media revealed that Eunjung was confirmed for the drama “Five Fingers”. However, on the 22nd of August, it was revealed that Eunjung had been dropped from the drama due to the bullying controversy surrounding T-ara. The Korean Actors Labor Union demanded that Eunjung be issued an apology by the producer and other crew members, saying “We are demanding that SBS and Yein E&M issue a sincere apology to member Ham Eunjung. The only way to restore her tarnished reputation is to essentially reveal the truth, and receive a genuine apology from all of you." The union also accused the PD of lying about the reason Eunjung was dismissed, giving the real reason for her dismissal as Eunjung's refusal to do product placements. In February 2013 Yein E&M issued a formal apology for firing Ham without notice.
From the group's debut in July 29, 2009 until September 2010, she was the first leader of T-ara. She, Hyomin and Jiyeon are the only three members of T-ara to be trained in acting. Instead, the three switched over to singing despite their original intentions.
^"티아라 은정 “이대 음대 나온 엄마께 죄송하고 감사해요” "I'm sorry, Mom, and thank you for your help". isplus. March 25, 2010. Retrieved January 2, 2011. "...Because of Eun-jeong her mother had to end her music career. Eun-jeong revealed in a March 24th interview with Daily Sports, "She was a graduate from Ewha Womans' University with a degree in music, she quit giving piano lessons to become my manager. Back then I didn't know much, but now I feel sorry," she said."