Kao shares his birthday with fellow Power Rangers Actress Thuy Trang (1973–2001), who played the original Yellow Ranger, Trini Kwan, in Mighty Morphin Power Rangers from 1993 to 1994.
Through the early 2000s, Kao may have been best known for his role as Archie Johnson in the hit television series CSI: Crime Scene Investigation, as well as the role of Kai Chen, the Blue Ranger, in Power Rangers Lost Galaxy. He has also appeared on TV shows such as Desperate Housewives (as Steve), ER (as Yuri), NBC's Heroes, Century City, Huff (as Kane), Power Rangers Wild Force (as General Venjix), Once and Again (as Steven), L.A. Firefighters (as Peter), Maybe This Time (as Takeshi) and more.
He was named one of People's "Hottest Bachelors" in 2006. Kao currently divides his time between Los Angeles and Beijing.
Kao wrote, directed and produced a short film entitled Initiation (2011), which starred Ashley Bell and Kao's CSI co-star Marc Vann. The film is about an Assassin trainee (Bell) who struggles with initiation day jitters under her mentor (Vann). Kao also produced and starred in a short film (as Jin) directed by Jerry Chan entitled Fast Money (2006).
Kao appeared as Sebastian in Wayne Wang's Snow Flower and the Secret Fan, and starred as the main romantic lead, Jefferson, in Quentin Lee's The People I've Slept With. Kao also played Edwin Luke, the brother of Keye Luke in Timothy Tau's short film bio-pic Keye Luke, which premiered at the 2012 Los Angeles Asian Pacific Film Festival and which was Closing Night Film of the inaugural 2013 Seattle Asian American Film Festival. Kao has recently signed on to a thriller film from China entitled The Deathday Party opposite Anita Yuen, which is also being shot in the ancient Chinese Alu Caves of Yunan. Kao played Shum in Michael Mann's film Blackhat (2015). Kao has also had roles in films such as The Hills Have Eyes 2 (as Han), Nomad: The Warrior (as Shangrek), When In Rome (as Nobu), and Jet Li's The One (as Woo).
In 2013, Kao joined the cast of the NBC TV series Chicago P.D. (a spin-off from Chicago Fire) as a series regular, a character named Detective Sheldon Jin who is in charge of surveillance at the Chicago Police Department Intelligence Unit.
On July 16, 2014, Kao and Zhou were officially married on stage after a charity event in Hangzhou, China.
