The $12 million upgrades involved a substantial realignment and the sealing of the dirt road.

The road, which connects the Golden Highway and New England Highway, also removes the need for traffic to travel via Scone, cutting about 44km off the journey.

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Liverpool Plains Shire Council (LPSC) mayor Andrew Hope said the link now provided a better drive for locals, tourists and stock and produce transport.

"An efficient freight industry is vital to rural and regional areas, and projects like the Willow Tree to Merriwa Road upgrade assist by cutting costs and boosting productivity in the transport sector with flow on benefits to our local primary producers," Cr Hope said.

"Individual motorists, families, school buses and emergency services also benefit from a safer, more efficient road system."

The upgrade was carried out by LPSC and Upper Hunter Shire Council with $5.5 million in funding through the federal government's Heavy Vehicle Safety and Productivity Program, $5.57 million from the state government's Restart NSW Fixing Country Roads program and $800,000 from its Regional Roads Repair Program.

Upper Hunter MP Michael Johnsen said the new route was a "beautiful drive" that "helps showcase our region".

"This sealing will save over an hour of travel time and make it easier for our farmers to get produce to market, along with opening up a tourist route that will enhance Merriwa, Willow Tree, and Quirindi businesses," Mr Johnsen said.

"[It] is a great investment in safety and freight times for our region."

New England MP Barnaby Joyce said the federal government funding formed a key part in developing the region's cattle and sheep markets.

"Just like the $2.8 million investment we're making toward the upgrade of the nearby Scone saleyards, our government is committed to strengthening our nation's livestock industry and this remarkable piece of engineering on the Merriwa-Willow Tree Road will deliver significant efficiencies to stock transport between the Liverpool Plains and Upper Hunter shires," Mr Joyce said.

Cr Hope thanked the council's engineering services department "in planning, developing, and overseeing the successful completion of this important project".

"It wasn't a simple case of slap on a bit of bitumen. In the last 3km to the top of the range, these works required a change in elevation of 200m and the movement of more than 30,000 cubic metres of rock and earth," he said.

Other projects in the LPSC area have included the bitumen sealing of Williewarina Road and rehabilitation of a 1.2km section of the Coonabarabran Road between Spring Ridge and Premer at 'Wheelabarrowback'.