Mubarak, 82, who has ruled Egypt for three decades, resigned following 18 days of demonstrations in downtown Cairo and across the country demanding his ouster.
Demonstrators in Gaza set off fireworks in support of their Egyptian cousins as thousands cheered in Cairo's Tahrir Square in celebration.
Twitter, the microblogging site, was filled with praise for the demonstrators and good wishes for the future. One participant tweeted, "Uninstalling dictator, 99 percent complete," followed by, "Uninstalling dictator COMPLETE - installing now: egypt 2.0."
The International Business Times reported among the first consequences of Mubarak's decision was a move by Switzerland to freeze his funds and those of 20 other Egyptian officials.
"Switzerland wants to avoid our financial center being used to hide funds illegally taken from the populations concerned," Swiss Foreign Minister Micheline Calmy-Rey said.
U.S. Vice President Joe Biden called the resignation "a pivotal moment in history."
"The future of Egypt will be determined by the Egyptian people. … The transition that is taking place must be an irreversible change and a negotiated path to democracy," he said during an appearance at the University of Louisville in Kentucky.
U.S. Sen. John Kerry, D-Mass., chairman of the Senate Foreign Relations Committee, issued a statement calling the developments extraordinary.
"Egypt's army and transitional leaders must heed the call to lift the emergency law and clarify a timetable to establish a proper foundation for credible elections," Kerry said. "The United States must help Egyptians turn this democratic moment into a process that builds a government responsive to economic needs as well as demands for freedom. What happens next will have repercussions far beyond Egypt's borders."
U.S. Sen. Ben Nelson, D-Neb., a member of the Senate Armed Services Committee, on MSNBC, called Mubarak's resignation "a welcome surprise" and speculated the "military must have stepped in," convincing him to resign.
British Prime Minister David Cameron urged Egyptians to establish "the building blocks of a truly open, free and democratic society," Sky News reported.
Arab League Secretary-General Amr Moussa, who has been touted as a possible presidential candidate, said he looks forward to building a consensus.
"There is a big chance now and a window has opened after this white revolution and after the president's concession," he said.
Israeli officials expressed hope the new regime would honor the Israeli-Egyptian peace treaty, and EU foreign policy chief Catherine Ashton said the alliance respected Mubarak's decision and called for broad-based discussions in the formation of a new government.
Al-Jazeera reported Qatari officials expressed hopes for "continuous special relations with Egypt that will benefit both countries" and quoted Bahraini Foreign Minister Khalid al-Khalifa as saying Egypt was taking the Arab world "into a new era."