On August 6, 1935, businessman Wee Kheng Chiang, together with six other friends, established the bank after raising S$1 million. The bank was named United Chinese Bank (UCB) to emphasize its links to the Chinese population in Singapore. On October 1935, UCB opened for business in the three story Bonham Building. In 1965, the bank was renamed to United Overseas Bank and opened its first overseas branch in Hong Kong. In 1970, UOB was listed on the Joint Stock Exchange of Singapore and Malaysia, at that time which Singapore did not have its own stock exchange. After it was publicly listed, the bank went through a series of targeted acquisitions. The bank first acquired Chung Khiaw Bank in 1971, which expanded its domestic presence and also gave the bank offices in Malaysia and Hong Kong. In 1973, UOB then acquired Lee Wah Bank, which provided services in Malaysia and Singapore. In that same year, the bank built a new 30 storey office tower in place of the Bonham Building, which was named the UOB Building (now known as UOB Plaza 2). The company continued with acquisitions, with Far Eastern Bank in 1984, Westmont Bank (now known as UOB Philippines) and Radanasin Bank (now known as United Overseas Bank (Thai) Public Company Limited) in 1999. The bank then took over the Overseas Union Bank Limited (OUB) in a takeover deal estimated to be worth S$10 billion in 2001.
In 2002, UOB started expanding into the Chinese market by opening a new full service branch office in Shanghai and upgrading of its Beijing office to a full-service branch.
Currently, United Overseas Bank Limited (commonly known as UOB) is a Singaporean multinational banking organisation headquartered in Singapore, with branches mostly found in most Southeast Asian countries. Founded in 1935 as United Chinese Bank(UCB) by Sarawak businessman Wee Kheng Chiang, the bank was set up together with a group of Chinese-born businessmen. The bank is the third largest bank in South East Asia by total assets. UOB provides commercial and corporate banking services, personal financial services, private banking and other asset management services, as well as corporate finance, venture capital, investment, and insurance services. It has 68 branches in Singapore and a network of more than 500 offices in 19 countries and territories in Asia Pacific, Western Europe and North America.

In December 2009, UOB opened its first branch in Mumbai, offering retail and wholesale banking services, including lending, treasury and trade finance products, to corporate, financial institutions and consumers. UOB provides a wide range of financial services through its global network of branches, offices, subsidiaries and associates: personal financial services, private banking, commercial and corporate banking, investment banking, corporate finance, capital market activities, treasury services, futures broking, asset management, venture capital management, insurance and stockbroking services. UOB also has diversified interests in travel and property management. In Singapore, UOB is a market leader in the credit card and private residential home loan businesses. It is also a key player in loans to small and medium enterprises. In 2011 UOB was named the Best Retail Bank in Singapore and the Best SME Banking Business in The Asian Banker's 10th International Excellence in Retail Financial Services Awards Programme. Its asset management arm, UOB Asset Management, is one of Singapore’s most awarded fund managers with a growing regional presence. UOB is rated among the world’s top banks, with a rating of AA1 from Moody’s and AA- from Standard & Poor’s respectively. UOB continues to be recognized as an excellent and professionally managed financial institution, earning a series of accolades and awards from leading publications and organisations in the financial services industry.