The unpopular US president led a series of speakers who described the Arizona senator as "his own man" and a great leader who understood the challenges facing America.
It was a clear attempt by the McCain campaign to accept an important strong endorsement from the sitting president while dismissing suggestions from Democratic rival Barack Obama that Mr McCain is inextricably linked to the failed policies of the Bush administration.
Under-fire vice presidential nominee Sarah Palin also won widespread support from speakers on the first full night of the Republican Party's national convention in St Paul, Minnesota.
Mr Bush said he knew from experience that Mr McCain was not afraid to say when he disagreed.
"John is an independent man who thinks for himself," he said.
"He's not afraid to tell you when he disagrees. Believe me, I know. No matter what the issue, this man is honest and speaks straight from the heart."
Mr Bush's support was a mixed blessing for Mr McCain - it will help him win more support from the party's conservative base but it will also tie him to the Bush administration's botched handling of Hurricane Katrina three years ago, which killed more than 1,800 people, and the unpopular Iraq war.
And the president's highly unusual cameo appearance via satellite from the White House seemed to acknowledge this.
Earlier this week, some Republicans had originally breathed a sigh of relief to have the unpopular president out of the way, dealing with Hurricane Gustav, when he cancelled his speech on Monday night
But in his rescheduled eight-minute speech, the president said Mr McCain's "independence and character helped change history" when he backed the so-called surge of US troops in the Iraq war last year, against public opinion.
"Some told him that his early and consistent call for more troops would put his presidential campaign at risk," Mr Bush said.
"He told them he would rather lose an election than see his country lose a war.
"That is the kind of courage and vision we need in our next commander-in-chief."
Mr Bush also addressed national security, a perceived strength of former Vietnam prisoner of war Mr McCain, and said the presidential hopeful understood the threats faced by America.
"We live in a dangerous world," he said.
"And we need a president who understands the lessons of September 11 2001: that to protect America, we must stay on the offence, stop attacks before they happen, and not wait to be hit again.
"The man we need is John McCain."
Mr Bush also weighed in on the debate over whether Mr McCain's running mate Mrs Palin had enough experience to be on the Republican ticket.
"When the debates have ended, and all the ads have run, and it is time to vote, Americans will look closely at the judgment, the experience, and the policies of the candidates - and they will cast their ballots for the McCain-Palin ticket," he said.
Later, an Obama campaign spokesman said Mr Bush "enthusiastically passed the torch to the man who's earned it" by supporting the president's policies.
Mr Bush's diminished role left Joe Lieberman, Democrat Al Gore's running mate in the 2000 election, at the top of the bill, capping an unprecedented political migration.
With stronger-than-expected criticism of Mr Obama, Mr Lieberman urged America to unite behind his long-time friend Mr McCain.
To chants of "USA, USA!", he said being an American was more important than being a Democrat or a Republican and added that he was supporting Mr McCain "because country matters more than party".
"God only made one John McCain, and he is his own man," he said.
He praised the Republican for advocating the surge of US troops in Iraq, and criticised Mr Obama for opposing it.
"When others wanted to retreat in defeat from the field of battle, when Barack Obama was voting to cut off funding for our troops on the ground, John McCain had the courage to stand against the tide of public opinion," the Democratic-turned-independent senator said.
He said Mr Obama was "a gifted and eloquent young man" but that "eloquence is no substitute for a record".
Mr McCain was the only candidate who had "shown the courage and the capability to rise above the smallness of our politics to get big things done for our country and our people", he said.
Mr Lieberman added that Mrs Palin, with whom he disagrees on the vast majority of issues, was "a leader we can count on to help John shake up Washington".
Former Law And Order actor Fred Thompson, who dropped out of the presidential race earlier this year, also praised Mr McCain as the "kind of character that civilisations from the beginning of history have sought in their leaders".
In contrast, he said to huge cheers that Mr Obama was only making history in so much as he was "the most liberal, most inexperienced nominee that ever run for president".
Mr Thompson said the US "needed a president who felt no need to apologise for the United States of America".
He added that the respect Mr McCain was given around the world was "not because of a teleprompter speech designed to appeal to American's critics abroad".
Mr Thompson also launched a strong defence of vice presidential nominee Mrs Palin and hailed her as a "breath of fresh air".
"She and John McCain are not going to care how much the alligators get irritated when they get to Washington, they're going to drain that swamp," he said.
Mr Thompson added that Mr McCain's decision to place her on the ticket "has the other side and their friends in the media in a state of panic".
Outside the Xcel Energy Centre, police used tear gas and flash-bang grenades to scatter an estimated 2,000 protesters who were allegedly trying to get past security fences.
The incident followed the arrests of nearly 300 protesters during outbreaks of violence in an anti-war March on Monday.
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