Malloch-Brown, who joined FTI in 2010 after serving in Gordon Brown’s Cabinet, will shift into an advisory role next month.
Kevin Hewitt and Chris Osborne, senior MDs for the firm’s corporate finance and economic practices respectively, will step in as co-chairs while retaining their existing roles.
Before serving in Cabinet Malloch-Brown had been vice-chairman of George Soros’ fund and foundation and was UN deputy secretary general under Kofi Annan in 2006.
Last year he and FTI paid compensation to international mining group BSGR Resources following a legal dispute after FTI resigned its contract to the group.
An FTI spokesman said that the move would allow Malloch-Brown "to focus more time on his numerous board-level and not-for-profit appointments."