ElBaradei, 71, was initially tipped to be the Prime Minister, but his nomination was rejected by the Salafist party Al-Nur.
ElBaradei was sworn-in on Sunday by interim President Adly Mansour as Egypt's interim vice president for foreign relations, the presidency said in a statement.
ElBaradei, former director of the UN's nuclear agency, is coordinator of the main alliance of liberal and left-wing parties and youth groups, known as the National Salvation Front, formed late last year after Morsi granted himself sweeping powers in a constitutional declaration.
The appointment of Nobel peace prize winner ElBaradei came after the military overthrew Islamist president Morsi on July 3.
Meanwhile, Prime Minister Beblawy is negotiating with nominees for the new Cabinet.
Nabil Fahmy, a former Egyptian ambassador to the US, accepted the post of foreign minister as part of the interim administration after current foreign minister Mohamed Kamel Amr decided not to continue in his post.
Amr had submitted his resignation to Morsi in solidarity with the demands of protesters who poured to the streets on June 30, demanding the Islamist leader's ouster.
The new Cabinet makeup is expected to be announced this week, media reports said.