The announcement came after the ethnic Albanian party, a parliamentary kingmaker, decided to back the Social Democrats (SDSM) in forming a government following weeks of horsetrading since an inconclusive early election in December.
However, a spokesman for the Democratic Union for Integration (DUI) said that the main ethnic Albanian party had yet to decide whether it would join a ruling coalition, leaving the possibility for a fragile minority cabinet.
"All options remain open ... It is not in our interest to take part in the government at any price," spokesman Bujar Osmani said.
After the DUI's decision, the SDSM said its top body unanimously confirmed Zaev as candidate for forming a new government.
Zaev now has to be officially named prime minister-designate by President Gjorge Ivanov.
"It is an honour, both mine and SDSM's, to get as soon as possible an opportunity to form a new democratic Macedonian government after 11 years of a regime," a party statement quoted Zaev as saying.
He was referring to former premier Nikola Gruevski, who stepped down a year ago after a decade in power to pave the way for new elections.
Macedonia's crisis erupted in February 2015 when a mass wiretapping scandal incited huge street demonstrations for and against the government, forcing the European Union to step in.
In the December vote Gruevski's conservative VMRO-DPMNE party secured 51 seats in the 120-seat parliament -- two more than the SDSM.
However, Gruevski has failed to reach a deal with ethnic Albanian parties.
Ivanov subsequently told Zaev that he would be appointed prime minister-designate once he secured the support of 61 MPs.
Two smaller ethnic Albanian parties, with eight MPs between 5them, have said they will back the SDSM, and with the support of 10 DUI deputies the party would have a majority.
EU Enlargement Commissioner Johannes Hahn hailed the developments. In a statement he called on Skopje to "enable a swift formation of a government that will address overdue reforms."
Ethnic Albanians make up around a quarter of Macedonia's population of 2.1 million.
Macedonia aspires to join both the EU and NATO.
But accession has been blocked by Athens owing to a dispute over the country's name, as Greece has a northern region also called Macedonia.
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