Lewis has already defected to The Sunday Times as business editor, replacing Rory Godson, who has taken the top PR job at Goldman Sachs.
Carr, currently world news editor, has been at the paper for two years and was formerly editor of the daily business features section, Inside Track.
In his new role Carr is responsible for the front page of the main paper but was not available for comment on his plans.
However, the FT's news operation has already been under review this year. In April, UK news editor Robert Shrimsley, who is responsible for half a dozen pages of domestic business news in the main section, pledged to 'humanise' the paper's coverage by putting in case studies where appropriate to illuminate stories.
Meanwhile, deputy news editor Tracy Corrigan, who was acting news editor in the place of Lewis, has been promoted to editor of the paper's online operation, FT.com.
She is handing over the news role to Carr before taking up her new post in January. She succeeds Chrystia Freeland, who will concentrate on being editor of Weekend FT. Freeland will do both jobs until the new year.
A major part of editor Andrew Gowers' strategy is to integrate the print and online operations.
Before joining the FT in May 2000, Carr spent 13 years at The Economist, most recently as business editor. He was also foreign correspondent, and reported on trade, environment, commodities and electronics.
Corrigan joined the FT in 1990 and has held a variety of jobs. In April she was made deputy news editor after three years of news editing the FT's US edition.
Prior to that, she was New York correspondent for three years. In 1994 she was made deputy editor of Lex, before which she had been head of the capital markets desk.