Baghdadi has been appointed caliph by the jihadist group, which has seized large swathes of Iraq and Syria.
The video appears to have been filmed on Friday during a sermon at the al-Nouri Mosque in Mosul, northern Iraq.
|Abu Bakr al-Baghdadi|
It surfaced on Saturday amid reports that he had been killed or wounded in an Iraqi air raid.
It was not clear when the attack was supposed to have taken place.
In the sermon, at Mosul's most famous landmark, Baghdadi praised the establishment of the "Islamic state", which was declared by Isis last Sunday.
Experts say the reclusive militant leader has never appeared on video before, although there are photographs of him.
"Appointing a leader is an obligation on Muslims, and one that has been neglected for decades," he said.
He also said that he did not seek out the position of being the caliph, or leader, calling it a "burden".
"I am your leader, though I am not the best of you, so if you see that I am right, support me, and if you see that I am wrong, advise me," he told worshippers.
Shi"ite volunteers patrol the area as they secure it against the predominantly Sunni militants from the Islamic State, previously called the Islamic State in Iraq and the Levant (ISIL), in the desert region between Kerbala and Najaf, south of Baghdad, July 3.
|Shia volunteers have stepped in for the Iraqi army in |
many parts of northern Iraq following the Isis advance
What is a caliphate?
An Islamic state ruled by a single political and religious leader, or Caliph
Caliphs are regarded by their followers as successors to the Prophet Muhammad and the leader of all Muslims
First caliphate came into being after Muhammad's death in 632
In the centuries which followed, caliphates had dominion in the Middle East and North Africa
The last widely accepted caliphate was abolished in 1924 by Turkish leader Kemal Ataturk after the collapse of the Ottoman Empire
Earlier on Saturday Iraqi Prime Minister Nouri al-Maliki fired two of his top security chiefs following the collapse of the Iraqi army in the north of the country last month.
The chief of the Iraqi army's ground forces as well as the head of the federal police both lost their jobs.
Meanwhile, extremists led by Isis destroyed at least a dozen shrines and places of worship in Nineveh province in northern Iraq.
|Shia Saad bin Aqeel Husseiniya shrine explodes in Tal Afar, Iraq|
More than a million people have fled their homes as a result of the recent conflict, and at least 2,461 people were killed in June, the UN and Iraqi officials say.
|A bulldozer destroys Sunni Ahmed al-Rifai shrine and |
tomb in Mahlabiya district outside of Tal Afar, Iraq