Veteran strongman Ali Abdullah Saleh, who arrived back from medical treatment in the United States in the early hours, is to formally hand over the reins of power in a ceremony at the presidential palace on Monday.
The handover will put the seal on a hard-won November transfer of power deal, under which Saleh agreed to step down in return for a controversial promise of immunity from prosecution over the deaths of hundreds of people during 10 months of protests against his rule.
The uprising split the security forces, left the two largest cities Sanaa and Taez divided into rival zones of control and sparked a loss of central government control that al-Qaeda loyalists exploited to seize large swathes of the south and east.
Hadi pledged that there were would be no let-up in the battle to wrest back the territory from the jihadists, in a country which was a key ally in the US war on terror before the Arab Spring-inspired protests against Saleh prompted Washington to begin to take its distance.
"It is a patriotic and religious duty to continue the battle against al-Qaeda," the new president said.
Hadi promised to restore security across his impoverished nation "without which no economic development would be possible." "If we don't restore security, the only outcome will be chaos," he said.
After a brass band played the national anthem, Hadi took the oath pledging to "preserve the country's unity, independence and territorial integrity."