Kwek's father, the late Kwek Hong Png left Fujian province as a penniless teenager for Singapore and subsequently founded the Hong Leong group there. Kwek Leng Beng was trained as lawyer in London, but chose to joined the family business in the early 1960s. He became chairman in 1990 and went on to establish an international reputation for his leadership of the Hong Leong Group, which is now a conglomerate with more than 300 companies, including 12 listed ones.

City Developments Limited, controlled by him, is a leading real estate developer in Singapore. It is an international company operating in 17 countries spanning Asia, Europe, North America and Australasia. The CDL Group has over 200 subsidiaries and associated companies including 8 companies listed on the stock exchanges of Singapore, London, Hong Kong, Amsterdam, New Zealand and Manila. CDL has a market capitalization of US$5.8 billion and ranks just outside Singapore's top 10 listed companies. It is also the second-biggest property developer in Southeast Asia.

Kwek Leng Beng also chairs Millenium & Copthorne (M&C) Hotels, which is a London-listed international hotel group of which 53% share belongs to CDL. M&C is ranked 40th among the world's top international hotel groups and has a portfolio of 88 hotels with close to 25,000 rooms in 16 countries.

Kwek's Hong Leong Group also owns Hong Leong Finance, which is Singapore's largest finance company, with a network of 28 branch offices.

Kwek Leng Beng is a member of the Board of Trustees of the Singapore Management University. He also holds an honorary doctorate (DUniv) from Oxford Brookes University.

Kwek oversees the Singaporean operations of the Hong Leong Group while cousin and fellow billionaire Quek oversees the Malaysian.