The formal nomination on Tuesday
sets up a two-month dash to the November elections that opinion polls show is a dead heat.
Bush was nominated at the Republican convention under way in New York when the delegation from Pennsylvania put him over the 1255 delegate-votes needed to lead the fight against the Democrats.
The nomination preceded the night's two featured speakers, first lady Laura Bush and California Governor Arnold Schwarzenegger, as Republicans hoped to show a softer, more compassionate side on the second night of their meet.
Meanwhile, raucous anti-Bush demonstrations continued to sweep New York.
About 125 people were arrested during all-day acts of civil disobedience. Another 100 people were arrested during a march from the former World Trade Center site to Madison Square Garden.
Outside the Hilton Hotel in Manhattan, a group of about 30 demonstrators dressed as pigs shouted "Halliburton thanks the GOP" while Republican delegates met inside.
Once headed by Vice-President Dick Cheney, Halliburton is the energy giant accused of raking in huge profits from contracts for "rebuilding Iraq".
Near Madison Avenue, a man who had lost his son in Iraq, posed with two anti-war activists at the entrance to the Roosevelt Hotel with a sign reading "Why go to Iraq if they die?"
In her speech, Laura Bush defended her husband's decision to go to war and insisted he was the best leader to lead America.
"My husband didn't want to go to war, but he knew the safety and security of America and the world depended on it," she said, describing Bush as "a loving man with a big heart".
Schwarzenegger - the star of movies such as Terminator - also drummed up support for the president, saying he must be re-elected to "terminate terrorism".
"He knows you don't reason with terrorists - you defeat them," Schwarzenegger said. "That's why America is safer with George Bush as president."