The agency, which won the business following a competitive pitch, previously handled Informa's financial PR until 2007, when Maitland took on the account.
FD's team is led by MDs Charles Palmer, John Waples and Tim Spratt.
Informa is a constituent of the FTSE 250 and is a specialist media and conference firm headquartered in London.
A mixture of organic growth and acquisitions under chairman and CEO Peter Rigby has left the firm just outside the FTSE 100.
Informa provides specialist information, conferences and courses to academics and businesses in fields such as insurance, law and finance.
The firm has 8,000 employees working in 150 offices in more than 40 countries. In 2008, Informa was in talks about a £3bn merger with rival media firm United Business Media, but negotiations were called off after a rise in Informa's share price made the deal uneconomical.
Maitland also advised the firm through a failed takeover bid later in 2008 by a private equity consortium of Blackstone Group, Carlyle Group and Providence Equity Partners.