The deal, which now runs until 2013 and is worth around £25m a year, may yet be extended by another four years.
Previously, Purple member Vestey Foods UK had supplied 10-man ration packs while individual ration packs were assembled by the Ministry of Defence in Portsmouth. But Vestey will now also supply the individual ration packs.
"This is great news for Purple and shows we are doing a good job and will continue to support the armed forces wherever they are in the world," said Purple MD Paul Dickinson.
Over the past two years Vestey has worked with the MoD to develop a multi-temperature ration pack designed to feed troops in Afghanistan and Iraq. This had helped it to retain the contract, Dickinson added.