She is also the wife of Minister Mentor Lee Kuan Yew in Singapore and a former pupil of Singapore's Methodist Girls' School and Cambridge University, where she was a Queen's Scholar from Malaya. In Lee's biography, he stated that he first met Kwa in 1944 at a party, and courted her from 1946. Kwa married Lee Kuan Yew on September 30 1950, and they have two sons and one daughter. Her eldest son is Lee Hsien Loong and her second son is Lee Hsien Yang. She has one brother, Dr. Kwa Soon Bee who retired as Permanent Secretary of the Ministry of Health, and two sisters, Mrs. Yong Nyuk Lin and the late Mrs. Earnest Lau.
During Lee's years as Prime Minister and Senior Minister, Kwa was frequently seen with her husband, especially on diplomatic trips and meetings with other foreign ministers. She suffered a brain haemorrhage in 2008.