Dr Keng graduated from the National University of Singapore in 1990 and started his basic surgical training in General Surgery in 1992 after finishing his national service. In 1995, he completed his Fellowship examinations from the Royal College of Surgeons, Edinburgh. He started to take an interest in Colorectal Surgery and began to focus his advanced surgical training in Singapore General Hospital, Department of Colorectal Surgery. He went to train under laparoscopic colorectal surgeon Professor John Monson in University of Hull, United Kingdom in 1998. When he came back, he focused on endoscopic colorectal techniques including colonic stenting and endorectal ultrasound in the accurate diagnosis of rectal cancers and subsequently their treatment. . He became a member of the American Society of Colorectal Surgeons in 2000. In 2001, he completed his exit examinations from the Academy of Medicine, Singapore. He became a consultant in the government hospital in the year 2002. In 2004, he left the public hospital and set up the private practice in Mt Alvernia Hospital as a Consultant Colorectal Surgeon in Digestive Health Associates Pte Ltd.

In the non medical field, Dr Keng is an active volunteer promoting the lives of people with deafness in Singapore since 1990. He interprets in sign language for the Deaf and received an award from the Ministry of Community Development and Sports in 2002. He actively supports school education among youths and sat in the School Advisory Committee for Bowen Secondary School from 2008 to 2011. He has an interest in the development of social entrepreneurship in Singapore.