A statement released by the campaign said that Bristol Palin will keep her baby and marry the child's father. Bristol Palin's baby is due in late December.
"Our beautiful daughter Bristol came to us with news that as parents we knew would make her grow up faster than we had ever planned. We're proud of Bristol's decision to have her baby and even prouder to become grandparents," Sarah and Todd Palin said in the brief statement.
The disclosure of the pregnancy came on the opening day of the Republican National Convention, scaled back because of Hurricane Gustav, and three days after McCain named Palin as his running mate. The other news was likely to overshadow the disclosure.
The first-term Alaska governor was in Minnesota preparing for her acceptance speech when the campaign issued the statement; her family was home in Alaska.
"Bristol and the young man she will marry are going to realize very quickly the difficulties of raising a child, which is why they will have the love and support of our entire family," they added.
The father was identified in the statement as Levi, but the campaign said it was not disclosing his full name or age or how he and Bristol know each other, citing privacy.
Sarah Palin's fifth child, a son named Trig, was born in April with Down syndrome. Internet bloggers have been suggesting that the child was actually born to Bristol Palin but that her mother, the 44-year-old Alaska governor, claimed to be the mother.
Palin spokesman Bill McAllister emphatically denied those rumors, and McCain adviser Mark Salter said the campaign announced the daughter's pregnancy to rebut them.
"Senator McCain's view is this is a private family matter. As parents, (the Palins) love their daughter unconditionally and are going to support their daughter," said McCain spokesman Steve Schmidt.
"Life happens," he said.
"An American family," added Salter.
The advisers said Palin told them about the pregnancy during lengthy discussions about her background. At several points during the discussions, McCain's team warned Palin that the scrutiny into her private life would be intense and that there was nothing she could do to prepare for it.
Advisers said Palin's daughter should be afforded privacy like the other candidates' children. Said Schmidt: "If people try to politicize this, the American people will be appalled."
In Monroe, Michigan, Democratic presidential nominee Barack Obama condemned rumors involving the children of candidates and echoed the McCain campaign argument. Said Obama: "I think people's families are off limits, and people's children are especially off limits."
Obama adamantly denied anonymous claims that his campaign helped spread the rumors.
"I am offended by that statement," Obama said. "Our people were not involved in any way in this, and they will not be. And if I ever thought that there was somebody in my campaign that was involved in something like that, they'd be fired."
Prominent religious conservatives, many of whom have been lukewarm toward McCain's candidacy, predicted that Palin's daughter's pregnancy would not diminish conservative Christian enthusiasm for the vice presidential hopeful, a staunch abortion opponent.
Focus on the Family founder James Dobson issued a statement commending the Palins for "for not just talking about their pro-life and pro-family values, but living them out even in the midst of trying circumstances." He added: "Being a Christian does not mean you're perfect. Nor does it mean your children are perfect. But it does mean there is forgiveness and restoration when we confess our imperfections to the Lord."
Roberta Combs, president of the Christian Coalition of America called the pregnancy private. "It's a matter that should stay in the family and they have to work through it together. My prayers go out to them."
Added Combs: "We're excited about the governor and think she's going to do well."
Mathew Staver, dean of Liberty University School of Law, said: "We're all sinners."
"We all make mistakes. Certainly, the ideal is not to get pregnant out of wedlock. But she made the right decision after her mistake," he said.
