Tett, currently assistant editor responsible for the FT's markets coverage, will take up her new role with immediate effect.
She succeeds Chrystia Freeland, who is leaving for a role at Thomson Reuters.
Tett, who was last year named Journalist of the Year at the British Press Awards, and who was Business Journalist of the Year at same event the year before, will move to New York full-time in September.
Her appointment comes as part of a mini editorial shake-up which last week brought the announcement of managing editor Dan Bogler's departure to become president and editor of Medley Global Advisors, a company bought by the FT Group earlier in the year.
Lionel Barber, FT editor, said: "Gillian's award-winning coverage of the global financial crisis has been recognised around the world.
"Having led the markets team from London, and with a wealth of global experience, she is ideally placed to lead the next phase of the FT's editorial development in the US.
"She will play an important ambassadorial role in the region and strengthen our growing influence in the North American market."
Tett joined the Financial Times in 1993 and has been capital markets editor, deputy editor of the Lex column, Tokyo bureau chief, Tokyo correspondent, London-based economics reporter and a reporter in Russia and Brussels.
Taken from Press Gazette: http://www.pressgazette.co.uk/story.asp?sectioncode=1&storycode=45113&c=1.