“We are ready to welcome you,” Jens Stoltenberg told reporters after meeting Prime Minister Zoran Zaev.
NATO members signed an accord in February allowing the ex-Yugoslav republic to become the 30th member of the U.S.-led group after a deal with Greece ended a long dispute over its name. The ratification process normally takes a year.
“It is important to commend North Macedonia for the reforms you have implemented,” Stoltenberg added.
Macedonia plans to raise defense spending to 2% of Gross Domestic Output by 2024 from 1% now.
Three other ex-Yugoslav republics - Slovenia, Croatia and Montenegro - have already joined NATO, as have other countries in the Balkan region including Albania, Bulgaria and Romania.
Russia says that by taking in Balkan members, the alliance is undermining security in the region.
The European Commission formally recommended last week that North Macedonia should start negotiations to join the bloc.