WFP's Executive Director Ertharin Cousin said the programme was "extremely grateful" for the aid, which brought the total raised to $88.4 million.
The kingdom pledged an additional $42 million for refugees in Ethiopia and $10 million for those in Kenya, the WFP said, amounting to a total of $104 million.
After the WFP appeal, Denmark, a big aid donor, had criticised wealthy Gulf states for failing to honour their promises on humanitarian aid for Syrians.
The WFP was forced last week to suspend the delivery of food vouchers for almost 1.7 million Syrians who have fled to Jordan, Lebanon, Turkey and Egypt.
It launched an unprecedented campaign on social media to raise $64 million to cover the month of December.
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The additional funds raised will help cover its needs going into January.
About $1.8 million was donated by individuals and private sector donors, and the rest by countries.
These include $10.2 million from Norway, $7.5 million from the Netherlands, $6.2 million from the European Union, $5.4 million from Germany, $2.1 million from Switzerland, $2 million from Qatar, $1.1 million from Ireland and $138,000 from Belgium.
Thanking all the donors, Cousin warned that funding would still be needed next year.
"As this increasingly 'hand-to-mouth' operation moves into winter, we are counting on our donors not to lose sight of the needs of these vulnerable people," she said.
"We are already focused on January, when the needs will be just as great."