Founded in 1921 as Australian Guarantee Company, Australian Guarantee Corporation (AGC) quickly became Australia's oldest national finance company, evolving from financing household items to specializing in motor vehicles, equipment, and personal loans. Registered as a public company in 1925, AGC was led by Managing Director Mr. G. K. Bain until 1956 and primarily funded its loans through public debentures.

The company forged strong ties with Ford Motor Company, establishing Traders Finance Corporation in 1925, and diversified further by forming an insurance subsidiary, Transport and General Insurance Company, in 1938. A pivotal moment came in 1957 when the Bank of New South Wales (later Westpac) acquired a 40% stake, progressively taking full ownership by 1988, which allowed the bank to engage in riskier lending beyond traditional banking regulations.

AGC expanded significantly, operating over 100 Australian branches by the mid-1970s and extending to 12 overseas countries, including New Zealand and Southeast Asia, by 1988. Despite their profitability, most international operations were eventually sold in the early 1990s as part of a business rationalization following the late-1980s financial crisis.