While the pact further cements a burgeoning grouping of major Sunni Muslim powers, there was no immediate clarity on each state's commitments, Reuters reported.
A Turkish official confirmed the agreement will be signed.
Turkey is a member of NATO. Saudi Arabia, another US ally, is one of the world's top oil exporters, while Pakistan is the only nuclear-armed Muslim country.
Turkish President Tayyip Erdogan and Pakistani Prime Minister Shehbaz Sharif, accompanied by powerful army chief Asim Munir, will meet Saudi Crown Prince Mohammed bin Salman in Jeddah for the signing.
The pact follows nearly a year of negotiations, reported by Reuters in January, and as the US-Israeli war of aggression against Iran exposes Persian Gulf states' security vulnerabilities and disrupts the shipping of oil and other key goods through the Strait of Hormuz.
Turkish Foreign Minister Hakan Fidan in January said that Ankara favored a broader regional security platform to promote cooperation and stability.
An existing Saudi-Pakistani pact treats an attack on either as an attack on both and encompasses "all military means", a Saudi official previously told Reuters.
The Pakistani military and government did not immediately respond to requests for comment.
Saudi Arabia's government did not immediately respond to a request for comment.