Launching her career in British firms Swire Group and HSBC Group, she was an Unofficial Member and then the Senior Member of the Executive Council and Legislative Council of Hong Kong in the 1980s and 1990s, witnessing the major events of Hong Kong including the Sino-British Joint Declaration and the Tiananmen Square protests of 1989.

In that capacity, she led missions abroad to promote Hong Kong textile and clothing products as well as stood firm against protectionism in her report for the Trade Policy Research Centre in 1983 on 'Protectionism and the Asian-Pacific Region'.

[3] She was also the director of the Mass Transit Railway Corporation from 1979 to 1985 and served as the chairman of the Prince Philip Dental Hospital from 1981 to 1987, during the formative years of the University of Hong Kong’s Faculty of Dentistry.

In May 1989, Dunn and several other Unofficial Members of the Executive and Legislative Councils presented the Basic Law Drafting Committee with a proposal for an "OMELCO Consensus" model for the post-1997 process of electing the Chief Executive, providing a moderate alternative to those put forth by the pro-democracy camp and the conservative hardliners from the business and professional community.

In a House of Lords debate in 1992, Dunn described having more directly elected seats as "unwise" and talked of it as "reviving uncertainty, tension and discord in our community."

In 1995, Dunn announced that she was retiring from Hong Kong politics, fueling speculation in the media over whether she still believed in the territory's future after 1997.

[8] While former British-appointed politicians found new favour with Beijing authorities in the run-up to 1997, Dunn bucked the trend by reinforcing her ties to Britain, retaining her seat in the House of Lords and maintaining high-profile positions in British companies, including HSBC Holdings.

After the passage of the Constitutional Reform and Governance Act 2010, she resigned from the British upper house in 2010 to preserve her "Non-Dom" status.

[9] For her services to Hong Kong, Dunn was made an OBE (Officer of the Order of the British Empire) in 1978, and then a CBE (Commander) in 1983.

One year later, she became the first ethnic Chinese and the first woman Hongkonger to be elevated to the British peerage in the Queen Elizabeth II’s 1990 Birthday Honours.