She replaces Philip Coggan, who became investment editor earlier this year.
Hargreaves' team of 15 journalists will cover London equities plus the world's stock, debt and currency markets, both online and in print.
'We are looking at redesigning and revamping markets coverage. That is my major priority. We should be a markets team for the FT with two different outlooks,' she said. At present, two-thirds of the team concentrates on the paper, with a third providing regular updates on the website.
'We are trying to deliver a summary with some analysis,' Hargreaves added.
'If people are taking money out of equity markets, what are they spending it on? A lot of market professionals look at the effect of the debt market, for example, on equity markets and currencies and so on. People are taking a much more global outlook and we have to reflect that.'
Hargreaves said PROs have a role to play in providing access to key figures: 'It is good to be put in touch, for instance, with people who are assessing the market, such as investment analysts.' But she added: 'We are not interested particularly in new products. It is very much market reporting, real business stuff.'
Hargreaves will report to financial editor Jane Fuller. Hargreaves' deputy is Paivi Munter, who is responsible for markets coverage on FT.com.
Hargreaves has worked for the FT since 1987, most recently as personal finance editor. Before that she was in Brussels for two years as EU correspondent. She began her career writing about the steel market for Metal Bulletin before moving to Reuters in New York.