Halliwell is responsible for promoting the city globally to the business and events market, leading a team of territory managers based in the UK and US.
She added that London & Partners will have closer links to the Mayor’s office, as well as the inward investment and business and educational communities.
Elsewhere at London & Partners, Andrew Cooke has been named chief operating officer and deputy chief executive; Paul Bromelow is sales director for foreign direct investment; Martine Ainsworth Wells is director of marketing & communications; Oliver Leeds is interim commercial director; Julie Chappell is acting head of digital.
London & Partners interim chief executive Danny Lopez said: "I am delighted to confirm the appointment of the executive team for London & Partners, the makeup of which, reflects the business objectives of the new agency. The executive, supported by their teams, can ensure that the excellent legacy of all three agencies is continued through London & Partners and that the capital remains the most popular place to visit, invest and study."