Ramping up agricultural production in a country known for being one of the world's biggest importers of rice, its national staple, would be among his priorities, Marcos told a news conference.
Tempering food price increases has become even more crucial for the Southeast Asian country as it battles inflation that reached its highest in more than three years in May.
"From the very beginning, I have always said that agriculture is going to be a critical and foundational part of our economic development or economic transformation as we anticipate the post pandemic economy," he said.
Though not unprecedented, it is unusual for a Philippine president to hold a post in their own cabinet.
Among his policy pledges in his election campaign, Marcos said slashing the price of rice by more than half to 20 pesos ($0.3704) per kilogram was his "aspiration".
Marcos, who was elected in a landslide and will be sworn in on June 30, warned of a food shortage that will push prices higher in the coming quarters, driven by "outside forces".
A food security crisis stoked by the Ukraine war has alarmed global leaders, including U.N. Secretary-General Antonio Guterres."The problem is severe enough that I have decided to take on the portfolio of secretary of agriculture at least for now, and until at least we can organize the department," he said.
Rolando Dy, agriculture economist and executive director of the Center for Food and Agribusiness at the University of Asia and the Pacific, said cutting local rice prices to 20 pesos per kg was "impossible."
"He has to rely on good advisers. He has to appoint competent undersecretaries for operations and high value crops," Dy said.