Mekdad, 66, had been deputy foreign minister since 2006. He has also held a string of diplomatic posts, including envoy to the United Nations.
Syrian President Bashar al-Assad also appointed Bashar al-Jaafari, currently ambassador to the United Nations, as deputy foreign minister.
Moalem was a staunch defender of Assad’s bloody crackdown on peaceful protesters in 2011, which sparked a conflict that has now lasted almost a decade.
Moalem died last Monday at the age of 79, after suffering years of heart problems.