This is the third time that Lau has won the Best Actor Award in his acting career.
"I'm honoured that the juries have been acknowledging my contribution to Hong Kong's film industry. I want to thank Deanie and [director] Ann. I couldn't have done it without you two," said the star in his acceptance speech at the Hong Kong Cultural Centre.
He added, "I've listened to many comments from people from different areas. I thank you all for supporting the movie. "A Simple Life" is just a very simple production. It's its sentimental value that makes it a delight to watch because it is relatable."
Ip, 64, whose portrayal of Tou Jie, a servant who spent her life serving her young master, Roger, in "A Simple Life", led her to beat younger actresses Shu Qi, Wei Tang, Gao Yuanyuan and Zhou Xun, and won her her first Best Actress award at the event.
"I'm glad to be able to receive this award in my 60s. I believe that this would be the last time for me to come up on this stage again. I don't think I could've made it without Andy and Ann's help. I also want to thank director Wong Jing who always encouraged me in my career," said Ip, who also won the Best Actress awards at the Venice Film Festival and Asian Film Awards for the same movie.
Meanwhile, Ann Hui, the director of the critically-acclaimed drama "A Simple Life", won Best Director for her efforts. Critics have claimed that the veteran was one of the biggest reasons for the movie's success.
"I would like to thank Hong Kong. I grew up here and I received my education here. This city has given me a lot of inspiration," said Hui.
Director Tsui Hark, who made a cameo appearance in "A Simple Life", also had reasons to celebrate, as his 3D movie "Flying Swords Of Dragon Gate", ended up winning five awards out of the 13 nominations.
Another highlight of the event would be the juries' recognition of "You Are The Apple Of My Eye", which won this year's new category – Best Mainland And Taiwan Film. The coming-of-age drama was screened in Malaysia last year.
Below is the complete list of winners:
31st Hong Kong Film Awards 2012 (Winner List)
Best Film : A Simple Life
Best Director : Ann Hui (A Simple Life)
Best Screenplay : Susan Chan (A Simple Life)
Best Actor : Andy Lau (A Simple Life)
Best Actress : Deanie Ip (A Simple Life )
Best Supporting Actor : Lo Hoi Pang (Life Without Principle)
Best Supporting Actress : So Hang Shuen (Life Without Principle)
Best New Performer : Hsiao Ching Teng (The Killer Who Never Kills)
Best Cinematography : Jake Pollock, Lai Yiu Fai (Wu Xia)
Best Film Editing : Yau Chi Wai (Flying Swords Dragon Gate)
Best Art Direction : Yee Chung Man, Lau Man Hung (Flying Swords of Dragon Gate)
Best Costume/Makeup Design : Willian Chang (Let the Bullets Fly)
Best Action Choreography : Yuen Bun, Lan Hai Han, Sun Jian Kui (Flying Swords of Dragon Gate)
Best Original Film Score : Chan Kwong Wing, Peter Kam, Chatchai Pongprapaphan (Wu Xia)
Best Original Film Song : Sandy Lam "Leung Sum Fa" (Hi, Fidelity)
Best Sound Design : Kim Suk Won (Flying Swords of Dragon Gate)
Best Visual Effects : Wook Kim, Josh Cole, Frankie Chung (Flying Swords of Dragon Gate)
Best New Director : Tsang Tsui Shan (The Big Blue Lake)
Best Film of Mainland & Taiwan : You Are the Apple of My Eye (Taiwan)
Lifetime Achievement Award : Ni Kuang (Screenwriter, Novelist)
Professional Achievement Award : Fong Ho Yuen (Cinematographer)