Seconds after the nationally televised announcement by Vice President Omar Suleiman, celebrations broke out in Cairo's central Tahrir Square, ground zero of the protest movement, which was packed with some 250,000 protesters.
"Egypt is free! Egypt is free!" the crowds shouted.
Car horns honked and people waved Egyptian flags, sang the national anthem and danced in conga lines.
"The Egyptian people made history today!" Hala Abdel Razik, a retired English teacher, told AOL News' Sarah Topol in Tahrir Square. "We still have a long way to go to fix things. We have to start all over again. It's the young people's role, with the help of older people. We're open to new scenarios."
In Washington, President Barack Obama said Egyptians "inspired us" through the "moral force of nonviolence" that changed their nation.
"The people of Egypt have spoken. Their voices have been heard. And Egypt will never be the same," Obama said.
Nobel Peace laureate and pro-democracy campaigner Mohamed ElBaradei said it was the "greatest" day of his life. "The country has been liberated after decades of repression," the former head of the International Atomic Energy Agency said, according to The Associated Press. He said he hoped for a "beautiful" transfer of power.
Related StoriesThat transition will be overseen by the High Council of the Armed Forces -- a group of generals headed by Defense Minister Mohamed Hussein Tantawi, 75 -- which is now in charge of the country. In a statement issued hours before Mubarak's resignation, the council promised that it would support free and fair elections. It also said it would scrap the much-hated emergency laws instituted when Mubarak took power in 1981, which grant police almost unlimited powers of arrest.
It is not yet clear what role, if any, Suleiman will have in the transitional regime.
Many Egyptians are shocked that Mubarak -- who is thought to have left Cairo earlier today and headed to his seaside palace at the Red Sea resort of Sharm el-Sheikh -- is finally out of their lives.
"I can't believe I'm going to see another president in my lifetime," Sherif el-Husseiny, a 33-year-old lawyer protesting in Tahrir Square, told Reuters. "I was born during [President Anwar] Sadat's time but was only 4 when he died."
The seemingly unmovable president was finally toppled by an uprising that grew from small groups of young activists organizing on the Internet. Google manager Wael Ghonim, 30 -- who set up a popular protest page on Facebook and is now seen as one of the revolution's figureheads -- told CNN that he wanted to thank Facebook founder Mark Zuckerberg for supplying the tools that helped mobilize masses of Egyptians.
The rebellion may have started online, but it soon spread throughout society. Inspired by events in neighboring Tunisia -- where a popular uprising ended President Zine El Abidine Ben Ali's 23-year-long rule -- Egyptians of all ages and classes took to the streets to protest Jan. 25.
They expressed their anger over the Mubarak regime's corruption and brutality, and its failure to create jobs and control soaring inflation. When the police used violence to break up the largely peaceful demonstrations -- at least 300 people are believed to have died in clashes over the past month -- they became angrier and more determined to overthrow the autocrat.
Mubarak desperately tried to cling to power during the 18 days of protest. He offered pro-democracy campaigners numerous concessions, including a promise not to run in elections in September. On Thursday, after word spread that he would resign, he went on national TV and announced he was handing only some of his powers to Suleiman.
But a surge in protests today apparently helped force the military to finally boot the 82-year-old autocrat from office.
More than 1,000 activists besieged the state TV and radio building in Cairo, in an attempt to end its broadcast of round-the-clock pro-Mubarak propaganda. Tahrir Square was crammed with a crowd that rivaled the quarter-million figure of the biggest protests over the past 18 days. Some 100,000 people gathered in the main square of Egypt's second biggest city, Alexandria.
And, for the first time since demonstrations began, protesters staged rallies outside the president's many palaces.
Throughout it all, the military stood by, guarding key pieces of infrastructure but keeping its earlier promise not to fire on protesters. When it became clear that the armed forces had taken over from Mubarak, protesters in Cairo embraced soldiers and had their pictures taken with tank drivers.
Although the future was not known, jubilation ruled for the moment.
"I'm excited, euphoric!" Nirvana Said, a training manager who has camped out in Tahrir Square since Jan. 25, told AOL News' Topol. "Now that the military controls everything, there will be no people on the square tomorrow. It's finished!"