Louis Koo also starred in various TVB television dramas, most notably the 1995 remake of Return of the Condor Heroes; Detective Investigation Files IV (1999); and A Step into the Past (2001). From the cool, aloof character that he had always been cast, he took a different character in A Step Into the Past. This deviation from the cool and aloof character to a funnier, carefree and down-to-earth one opened his career to an extensive list of romantic comedy movies that now have a distinctive Louis Koo element. His silent and sincere attitude, and his devotion to his family, makes his characters more convincing, and thus earns him a wide range of fan base. He further sang a couple of theme song for the television series that he played in. Besides that, he also has various other songs. A notable one is the album "Mr.Cool".
The 2007 film, Happy Birthday, introduced a sensitive character portrayed by Louis Koo. What sets this movie apart from his other romantic movies is the serious tone between dialogues. This is another first in Louis Koo's film career, that is to portray a sensitive man sans the comical gestures he has always done in past romantic comedies.
His most recent screen character as a drug addict in Protégé transcended from his usual charm and wit performances, as he attempted to forego his hunky image. Little screen time did not stop him to successfully achieve this role, and thus earned him positive feedback tucked under his belt.
Koo later received international acclaim for his performance in Election 2 (aka Triad Election ), which was screened during the Out of Competition (midnight screenings) section at the Cannes Film Festival in 2006.
He won the award for Most Beloved Actor in the Hong Kong UA Film Awards 2006 through public voting for his role in Election 2.
In the summer of 2001, a young boy went into a coma and Louis visited his little brother to encourage him to have faith.