Mok was born on 2 June 1970 as Karen Joy Morris in Hong Kong and is the sister of the writer and producer Trevor Morris, and a granddaughter of Alfred Morris, the first principal of King's College, Hong Kong. She speaks English, Cantonese, Mandarin, Italian, German and French.
She is of mixed ancestry: her father is half-Chinese and half-Welsh, while her mother is half-Chinese, quarter-Iranian, and quarter-German. Mok attended Diocesan Girls' School from primary to secondary grade in Hong Kong. When she was a F.5 student, she received the 1st Hong Kong Outstanding Students Awards. She later left Hong Kong in 1987 and studied abroad. She attended United World College of the Adriatic near Trieste, Italy from 1987 to 1989, and majored in Italian literature when studying at Royal Holloway, University of London.
In her initial Hollywood productions such as Around the World in 80 Days (2004) Mok used her birth name Karen Joy Morris, but went to using her stage name Karen Mok for all future productions such as Man of Tai Chi (2013) . She also supplied the voice of Princess Kida for the Cantonese dub of Walt Disney's Atlantis: The Lost Empire (2001). Mok played the female lead in the 10th anniversary Asian tour of the hit Broadway musical Rent in the lead role of Mimi in 2005 and 2006.
Mok carried the torch at the 2008 Summer Olympics held in Beijing and performed at the opening and closing ceremonies. In October 2008, she launched her own brand of perfume in Hong Kong.
Mok conducted a number of international concert tours, the most recent ones being The original Karen Mok show (2011/2012), The Age of MOKnificence (2014/2015) and the world tour REGARDEZ (2015/2016). She was the first Chinese pop artist to give solo concerts in Madrid and Milan. For her tour REGARDEZ, she also acted as concert director.
Mok has completed many endorsement agreements with leading brands such as Canon, Kappa, Cadillac, Clear, Chow Tai Fook, Lux, Titus, and Mandarin Oriental.
In 2016, she starred in the two reality TV shows "Up Idol" (我们来了), of Hunan Television and "The Next" (天籁之战), of Dragon Television
Mok married her first boyfriend, German-born Johannes Natterer, at a church near Florence, Italy, on 1 October 2011. Mok has 3 step-children and spends her time between London and her international engagements.
Mok is a strong advocate for animals and animals rights and has been involved in numerous campaigns for this purpose. Amongst others, she has joined efforts to help bears in China whose bile is used for medicinal purposes and has been on an expedition with Hong Kong Society for the Prevention of Cruelty to Animals (SPCA) to demonstrate against culling of baby seals. She has also been involved with the People for the Ethical Treatment of Animals Asia-Pacific's (PETA).
In 2007, Mok was involved with MTV EXIT, a campaign against human trafficking in Asia. She presented Traffic: An MTV EXIT Special, a documentary on trafficking. Karen currently serves as ambassador for UNICEF, SPCA, Animals Asia Foundation, Enlighten-Action for Epilepsy, Care for Children, and Roll Back Malaria (RBM).
In 2016, she was awarded the title of the cultural ambassador of the Italian city of Bergamo, being the first Chinese artist being awarded such a prize in Italy.