Radev's Progressive Bulgaria looks set to win at least 130 of the 240 seats in parliament.
This comes after the country held eight elections in five years, which resulted in divided parliaments with coalition governments that quickly collapsed.
Radev is more Eurosceptic than previous winners and critical of the country's arms support for Ukraine. The election result also means that he does not need support from the pro-Russian far right.
"He is signaling that he wants to continue a pro-European policy and not block the EU. The question now is whether those signals are followed through," analyst Daniel Smilov told AFP.
Calls from Radev for "dialogue" with Russia are simultaneously welcomed by Moscow.
