In a confident speech delivered after he took the oath of office at a red carpet ceremony in Damascus, Assad branded the 2011 Arab uprisings a "fake spring".
Assad, 48, won a June election denounced as a "farce" by his detractors as it was staged more than three years into a devastating war that has killed more than 170,000 people and uprooted millions.
"Syrians, three years and four months ... have passed since some cried 'freedom'," Assad said, referring to the 2011 revolt.
"They wanted a revolution, but you have been the real revolutionaries. I congratulate you for your revolution and for your victory," Assad told his supporters.
"Those who lost their way can now see clearly ... the monstrous faces have been unveiled, the mask of freedom and the revolution has fallen."
Rebel mortar fire hit several districts of Damascus, as Assad ended his speech, residents said. State media said four people were killed.
Assad's inauguration comes with much of the world's attention focused elsewhere, as violence engulfs Iraq and Gaza, even though his forces continue to pound rebel-held areas of second city Aleppo.
During the first two years of the Syrian revolt, which began as a peaceful protest movement before transforming into an armed rebellion, the opposition's Western and Arab supporters repeatedly insisted he must step down.
But the rise of the Islamic State (IS) in both Syria and neighbouring Iraq has turned the tide.
Assad has repeatedly branded the revolt as a foreign-backed "terrorist plot", refusing to recognise any genuine movement for change.
Assad won the election, held in government-controlled areas only, with 88.7% of the vote, defeating two other candidates seen as figureheads, rather than genuine challengers.
He issued a fresh call on Wednesday for "national dialogue", but warned against talks with "those who have not proven their patriotism", referring to the exiled opposition.
"We stress the need to press on with national reconciliations to stop the bloodshed," he added, referring to a string of local truces reached around Damascus that activists have said remain fragile.
The opposition National Coalition branded the election a "farce" even before it was held, in a statement later echoed by US Secretary of State John Kerry and Nato chief Anders Fogh Rasmussen.
Samir Nashar, a veteran dissident and member of the coalition, admitted the world's attention has since turned away from Syria.
"Unfortunately for Syrians, the instability (across the Middle East) has distracted the international community's attention," he said.
Analysts say the rise of the militants has been a "gift" for Assad, who will try to take advantage of the West's fear of extremism and present himself as a bulwark against it.
Following in the footsteps of his father and predecessor Hafez, who ruled Syria with an iron fist for 30 years, Assad has ignored the calls for his ouster.
After the inauguration, the government has to resign and Assad will appoint a new prime minister to replace Wael al Halqi.
But for the new exiled opposition chief, Hadi al Bahra, Assad "is at the core of the Syrian conflict (and) is still the main reason behind the unprecedented humanitarian crisis that is affecting the country."
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Sorry but I can't support a man with so many dead children's blood on his hands...his days are numbered. Equally hate most of the rebel groups too...what they bringing? peace? or too busy murdering innocents and people over stupid reasons and now trying to have a holy war in Iraq (bunch of wusspuss) just have to pray to Allah Almightly a solution soon comes to all this restlessness.
."Analysts" say the rise of the militants has been a “gift” for Assad, who will try to take advantage of the West’s fear of extremism and present himself as a bulwark against it." Question: who is the "analyst", the true fact is that Assad was always correct when he implicated these thugs fighting, killing and blowing up civilians in Damascus as extremists funded by the Gulf states with the support of our government. If Assad falls, beware, the Wahabi brand of Saudi's will overtake Syria, Lebanon, Iraq with no mercy for dissent. Why are we supporting these brutal terrorists against Assad? simple, it's a leverage against Iran, who realistically poses no danger to US, go figure?
"Analysts" say the rise of the militants has been a “gift” for Assad, who will try to take advantage of the West’s fear of extremism and present himself as a bulwark against it." Question: who is the "analyst", the true fact is that Assad was always correct when he implicated these thugs fighting, killing and blowing up civilians in Damascus as extremists funded by the Gulf states with the support of our government. If Assad falls, beware, the Wahabi brand of Saudi's will overtake Syria, Lebanon, Iraq with no mercy for dissent. Why are we supporting these brutal terrorists against Assad? simple, it's a leverage against Iran, who realistically poses no danger to US, go figure?