Kim Chiu launched her career by winning Pinoy Big Brother: Teen Edition. She was its first winner, beating 14 housemates. Kim and the rest of the housemates entered theBig Brother house on April 23, 2006. After 42 days of spending summer in the Big Brother house, Kim was named the Teen Big Winner with 626,562 votes (41.4% of the total votes) at the Aliw Theater, Cultural Center of the Philippines Complex in Pasay City on June 3, 2006. Kim was a junior high school student at the Distance Learning Center of ABS-CBN, the network's school for their young artists. She was the only housemate who was never nominated for eviction. Chiu sang a Chinese song called "朋友" ("Friend") by Emil Chau in Big Brother's house.
In the six months since the end of Pinoy Big Brother: Teen Edition, Chiu and Gerald Anderson have appeared together in several shows on the ABS-CBN network, did several commercial endorsements, and appeared in their first movie, First Day High. Chiu and Anderson also appeared in Love Spell and Aalog-Alog. Their love team was named "Kimerald" by the fans, which is a portmanteau of their names. They marked their first anniversary in show business with their first starring movie I've Fallen For You which premiered September 26, 2007 under Star Cinema.
Chiu starred in her first primetime TV series entitled Sana Maulit Muli, where she is once again partnered with Anderson. The series started airing in the Philippines on ABS-CBN in 2007. Chiu is a member of ABS-CBN's circle of homegrown talent called Star Magic. She is currently a regular performer on ASAP '09 and was the leading lady in the prime time show My Girl, the Filipino remake of the Korean series with the same title. She also starred with Claudine Barretto in the mini series Maligno.
In January 2009, Kim starred in the TV series entitled Tayong Dalawa which was Kim's third appearance on a primetime TV series and the second time she worked with Gerald Anderson and Jake Cuenca since Sana Maulit Muli. Kim was a special guest in 2009 Philippine Fiesta along with Gerald Anderson, held on August 15-16 at Meadowlands Exposition Center Secaucus, New Jersey. Chiu will also star in Star Cinema's official entry to the 2009 Metro Manila Film Festival, I Love You, Goodbye.
In 2010, Chiu will be part of new drama series, Kung Tayo'y Magkakalayo, starring Gerald Anderson, Gabby Concepcion, and Kris Aquino. Her second movie with Anderson will be released as Star Cinema's opening movie release for 2010.