His father, Reverend Khoo Cheng Hoe, was a pastor of the Chinese Methodist Church at Madras Lane, Penang, and his mother, Kwan Chin Poh, was studying at the Eveland Seminary in Singapore before marriage in March 1919.

[1][7] In October 1951, Khoo left for United Kingdom to further his studies in medicine, specifically on dermatology, neurology, and chest-related diseases.

[1] In 1965, Khoo succeeded Ernest Steven Monteiro as the professor of clinical medicine, and pushed for the establishment of a S$4 million institute for medical specialties at the University of Singapore.

[14][15] As such, on 7 April 1969, the National Kidney Foundation was inaugurated by Minister for Health Chua Sian Chin, with Khoo being elected as the founding chairman.

[19] His good class bungalow at Caldecott Hill was put up for sale by his estate on 15 August 2012, and was sold for S$26.1 million on 30 October 2012.