CNN) -- Sen. Barack Obama has selected Sen. Joe Biden as his running mate, according to his official Web site and a text message the campaign sent to supporters early Saturday.
Barack has chosen Senator Joe Biden to be our VP nominee," the text message, sent at about 3 a.m. ET, said.
Word that Biden's was Obama's choice first came earlier Saturday morning when Democratic sources confirmed the decision to CNN.
Obama was expected to appear with Biden at a Saturday afternoon rally in Springfield, Illinois.
Biden was long considered a likely choice for vice president, but the buzz surrounding him intensified after he returned earlier this week from a two-day trip to the Republic of Georgia after Russian troops invaded.
Biden, chairman of the Senate Foreign Relations Committee, brings years of experience that could help counter GOP arguments that an Obama administration would be inexperienced on foreign policy.
Sen. John McCain's campaign quickly reacted to word that Biden would be Obama's running mate with a dig at Obama's foreign policy credentials.
"There has been no harsher critic of Barack Obama's lack of experience than Joe Biden," McCain campaign spokesman Ben Porritt said in a written statement.
Biden has denounced Barack Obama's poor foreign policy judgment and has strongly argued in his own words what Americans are quickly realizing -- that Barack Obama is not ready to be president."
In a debate during the Democratic primary contest, Biden raised questions about Obama's foreign policy experience.
"Who among us is going to be able on day one to step in an end the war? Who among us understands what to do about Pakistan? Who among us is going to pick up the phone and immediately interface with Putin and tell him to lay off Georgia because Saakashvili is in real trouble. Who among us knows what they're doing? I have 35 years of experience," Biden said.
During another debate, moderator George Stephanopoulos referred to some of Biden's comments on Obama.
"You were asked, 'Is he ready?' You said, 'I think he can be ready, but right now, I don't believe he is. The presidency is not something that lends itself to on-the-job training,'" Stephanopoulos said.
"I think I stand by that statement," Biden replied.
Biden, in a July interview, said he would choose Obama's judgment over John McCain's war record and foreign policy experience.
"But 20 years of experience that has not been very solid in terms of projecting what was going to happen just doesn't make you a better commander-in-chief," Biden said. "We don't need as a commander-in-chief a war hero. John's a war hero. We need someone with some wisdom."
Biden abandoned his own White House run after a poor showing in Iowa's first-in-the-nation caucuses. He also ran for the 1988 Democratic presidential nomination but dropped out after charges of plagiarism in a stump speech.
The 65-year-old was first elected to the Senate in 1972. Shortly afterwards, his first wife and daughter were killed in a car accident. He considered resigning, but decided to continue with his political career.
Biden is currently serving out his sixth term, making him Delaware's longest-serving senator.
Biden is married and has three children. He received his undergraduate degree from the University of Delaware and got a law degree from Syracuse.
In 1988, Biden suffered an aneurysm and nearly died but has recovered fully.
One of Biden's grandfathers was a Pennsylvania state senator, according to the Almanac of American Politics.
News of Biden's selection came after word that three Democrats who had been considered contenders, New York Sen. Hillary Clinton, Indiana Sen. Evan Bayh and Virginia Gov. Tim Kaine, had been ruled out. The two Democratic sources who told CNN that Obama had chosen Biden spoke on the condition of anonymity.
Biden will make his first big speech as the vice-presidential candidate on Wednesday, August 27 -- the third night of the Democratic convention