A Hakka, Kate Tsui was born and raised in Hong Kong. Her father works in logistics, and while her mother is now a homemaker, she was a dancer when she was younger. Tsui also has an older sister, who is married with two kids. As of 2014, Tsui has expressed that with the exception of herself, her entire immediate family now resides in Taiwan.

Aside from her development in television acting, Tsui also experienced success in developing her career in the film industry. In 2007, through a series of auditions, Tsui was cast as the female lead, alongside A-list actors Tony Leung Ka-fai and Simon Yam, in Eye in the Sky, which is a film produced by Johnnie To and directed by Yau Nai-hoi. With her performance in the film,  Eye in the Sky was praised by professional Hong Kong film critic, Sek Kei, as the best Hong Kong film in the first half of 2007. The film was subsequently entered into the Berlin International Film Festival, as well as the Shanghai International Film Festival. Through her performance in the film, Tsui was widely acclaimed to be talented in acting and a rising actress worth looking out for.  With her performance in Eye in the Sky, Tsui earned the Best Newcomer - Gold Award from Hong Kong Film Directors' Guild 2007, as well as Hong Kong Film Award for Best New Performer from the 27th Hong Kong Film Awards, held in 2008. The latter is a particularly outstanding achievement, for Tsui is, so far, the only individual to have received a Hong Kong Film Award, while being fully contracted by TVB, since Anita Yuen, who coincidentally is also a Miss Hong Kong pageant winner, won the same award back in 1993.  Professional Taiwanese film critic, Mai Ruoyu, had openly criticized the Golden Horse Film Festival and Awards, a film festival and awards ceremony held in Taiwan, for excluding Tsui and her performance in Eye in the Sky from a nomination in the Best New Performer category. He had further praised that Tsui has the most potential and talent in acting among all of TVB's Miss Hong Kong-turned-actresses, since Maggie Cheung.

What happened to her in 2007?
In 2007, through a series of auditions, Tsui was cast as the female lead, alongside A-list actors Tony Leung Ka-fai and Simon Yam, in Eye in the Sky,