The actor, in his role as UN ambassador, helped to launch its $40m (£32,2m) International Fund for Agricultural Development on Monday.
The fund is intended to help support farmers and food producers in rural areas globally during the pandemic.
"It is about food," the Luther star told BBC News.
"It is about the basic necessity for human beings, and that will run out if the farmers can't farm."
Idris, and his wife, model and fellow activist Sabrina Dhowre Elba, have been quarantined in their London home since last month, having tested positive for coronavirus.