Jim Moseley, who is also a former FDF president, will fill the position while a permanent successor is found for Leech.
Leech will take over as boss of the British Property Federation in the New Year.
Moseley said he looked forward to continuing the progress made by Leech during his time in charge.
FDF president, Richard Evans, said he was delighted to welcome Moseley back to FDF.
“This is an important time for the sector and he has a wealth of industry experience and a knowledge of the FDF that equips him well to see the federation through until we have a permanent director general in place.”
Meanwhile, last week, Leech told delegates at Food Matters Live that there needed to be a clear strategy between industry and government to spread a single message about health to consumers.