Nabil Fahmy, a former Egyptian ambassador to the United States, accepted the post of foreign minister on Sunday as part of the interim administration formed in the wake of President Mohamed Morsy's overthrow on 3 July.
The announcement comes the same day Egypt's current Foreign Minister Mohamed Kamel Amr decided not to continue in his post.
Amr had said he believed the new stage of transition required a new minister, adding that he will continue to run ministry affairs until a replacement is appointed.
Prime Minister Hazem al-Beblawy is meanwhile continuing negotiations with nominees for the new Cabinet following the ouster of ex-President Mohamed Morsy on 3 July.
The new Cabinet makeup is expected to be announced this week.
Amr had submitted his resignation to Morsy in solidarity with the demands of Egyptian protesters who poured to the streets on 30 June to demands early presidential elections.
Leftist politician Gouda Abdel Khaleq said on Sunday that he declined an offer to return to the post of minister of supply in Egypt's interim government, citing personal reasons.
Two sources in Egypt's transitional administration had earlier said Interim Prime Minister Hazem al-Beblawy would ask Abdel Khaleq to serve in the post.
"I was offered the post by Beblawi, but I declined for personal reasons," he told Reuters over the phone. Abdel Khaleq had held the post before for a few months in 2011.