The Portuguese football manager will hope to use his status to raise awareness of the humanitarian agency's work and to champion the zero hunger challenge, which aims to eliminate hunger.
His wife Matilde has been appointed as a special ambassador for school feeding.
Mourinho is set to visit WFP operations in sub-Saharan Africa in the coming weeks.
The 51-year-old said: "Supporting the work of the World Food Programme on the front lines of hunger is a personal decision about a cause that is very close to the hearts of me and my family.
"If we can harness the spirit and the will to address the nutritional needs of the poor, then we have a real chance of ending hunger in our lifetimes."
According to the WFP, some 842 million people do not have enough food to eat and poor nutrition causes nearly half of all deaths among children aged under five.
Amir Abdulla, WFP deputy executive director and chief operating officer, said: "Jose Mourinho has achieved almost every success at the top of the game of football and we are delighted that he is now taking on a new challenge to help us reach zero hunger.
"We need strong, respected and committed partners to help us eliminate hunger in our lifetimes and I have no doubt Jose will deliver in his role as a WFP ambassador against hunger."
Mourinho joins a host of celebrities and athletes who are WFP ambassadors against hunger, including actress Drew Barrymore, singer Cristina Aguilera and footballer Kaka.
Mr Abdulla added: "Our team of ambassadors against hunger provide a powerful voice for the hungry. Their status and the support they draw among millions of fans around the world helps us to get the message out that reaching zero hunger is an achievable target and the right target for our times."