Nato states are due to sign an agreement with Macedonia, clearing the way for the Balkan nation to become the military alliance's 30th member.
Each Nato member will then need to ratify the accession protocol.
This comes after Greece's MPs last month backed a deal ending a 27-year row over its northern neighbour's name.
They approved the name Republic of North Macedonia. Greece had blocked Macedonia's membership saying the name implied territorial ambitions.
The Greek region of Macedonia includes the country's second city Thessaloniki. Greek lawmakers approved the deal despite widespread opposition from the public.
The prolonged dispute meant that until now Greece also frustrated Macedonia's drive to join the European Union.
It will be signed on Wednesday at a ceremony in Brussels - the headquarters of Nato.