Kara debuted as a quartet on M! Countdown in March 2007 with their debut single "Break It" from their first studio album entitled The First Blooming. In early 2008, however, member Kim Sunghee left the group due to parental pressure. She was eventually replaced by Goo Hara and Kang Jiyoung, and the group made their comeback as a quintet with "Rock U" in July 2008.
Due to Kara's debut album The First Blooming being relatively unsuccessful, Han went on to participate in many variety shows from late 2007 to early 2009 in order to keep the group recognizable to the public. She was the VJ for MSL Break from 2007 to 2008. She replaced Tiffany of Girls' Generation as co-host of Boys and Girls Music Guide in June 2008 with Kim Hye-sung, and later with actor Kim Soo-hyun. Their segment ended on May 8, 2009. From October to December 2008, she was part of the cast of the MBC Every 1reality showI Need a Family - Season 2, where a group of celebrities would live life as a family, consisting of a father, mother, son and daughter. She also became part of MBC's entertainment news show Section TV as a "pop correspondent," debuting on November 21, 2008. On July 31, 2011, she became a co-host of SBS's Animal Farm.
Han was featured on rapper Nassun's single "Come to Play," which was released in March 2009, and was featured on the soundtrack for the movie Why Did You Come to My House? (2009), releasing her first solo song entitled "Miracle." In October 2009, she became part of the "Dream Team Girl Group" named 4Tomorrow for Samsung's campaign Samsung Anycall. Their digital single "Tomorrow" was released on October 6, and the official music video for their single was released on the October 12, starring actor Lee Dong-gun. In 2010, she recorded the song "Super Star" for the soundtrack of the KBS2 drama Mary Stayed Out All Night (2010). She performed the song as one of her solos during the South Korean leg of Kara's tour entitled Karasia in February 2012. In 2011, she recorded the song "Because of Love" for the soundtrack of the SBS drama Warrior Baek Dong-soo (2011).
In January 2012, it was announced that each member of Kara would be recording solo material for their upcoming concerts, and it was later revealed that Han's song was entitled "Guilty". She performed her solo song during the group's tour along with the other members and their respective solo songs. The Japanese version of "Guilty" was later included in Kara's special album Kara Collection in September 2012. It was released digitally in Japan on August 26, with the video being released on September 4. The Korean version of the song was included in the group's compilation albumKara Solo Collection, which was released on December 4 in South Korea. The track was released digitally on November 30 along with its respective music video. She made her solo debut with "Guilty" on MBC's Music Core on December 15.