The European Union has already agreed deals with Egypt, Tunisia, Mauritania and other countries meant to help stem flows of irregular migrants.
"I can announce a financial package of $1 billion for Lebanon that would be available from this year until 2027," von der Leyen said, adding that "we want to contribute to Lebanon's socio-economic stability".
The European Commission president said the aid was designed to strengthen basic services such as education and health in the country mired in a severe economic crisis.
She called for the adoption of reforms, saying: "Lebanon needs a positive economic momentum to give opportunities to its businesses and citizens."
Von der Leyen said the EU was committed to maintaining "legal pathways open to Europe" and resettling refugees to the bloc, but added that "at the same time, we count on your good cooperation to prevent illegal migration and combat migrant smuggling".
Lebanon's economy collapsed in late 2019, turning the country into a launchpad for migrants, with Lebanese joining Syrians and Palestinian refugees making perilous voyages bound for Europe.
The authorities in Beirut say Lebanon currently hosts around two million people from neighbouring, war-torn Syria -- the world's highest number of refugees per capita -- with almost 785,000 registered with the United Nations.
"We understand the challenges that Lebanon faces with hosting Syrian refugees and other displaced persons," said von der Leyen, adding the EU had supported Lebanon with 2.6 billion euros to host those people.
The war in Syria that erupted in 2011 after the government repressed peaceful pro-democracy protests has killed more than half a million people and displaced around half of the pre-war population.
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