The group said Obama was the choice of 70.4 percent of its members who cast votes online, Politico.com reported. About 300,000 people, roughly 10 percent of the membership, participated.

"In just a few years, the members of MoveOn have once again demonstrated that real change comes not from the top-down, but from the bottom-up," Obama said as he accepted the endorsement. "From their principled opposition to the Iraq war -- a war I also opposed from the start -- to their strong support for a number of progressive causes, MoveOn shows what Americans can achieve when we come together in a grassroots movement for change."

MoveOn was started 10 years ago by two computer entrepreneurs with an online petition that urged Congress to censure President Bill Clinton "and move on" as an alternative to impeachment.

The endorsement gives Obama access to the MoveOn e-mail list, which includes millions of names.