U.S. Vice President Joe Biden said Wednesday he has decided not to run for president next year, a decision expected to bolster the chances of former Secretary of State Hillary Clinton winning the Democratic nomination.

"As my family and I have worked through the grieving process, I've said all along what I've said time and again to others, that it may very well be that that process, by the time we get through it, closes the window on mounting a realistic campaign for president, that it might close," Biden said during an announcement at the White House, speaking of the death of his late son.

"I've concluded it has closed," he said, flanked by President Barack Obama on his right and his wife Jill Biden on his left.

Biden also said he believes he's out of time, "the time necessary to mount a winning campaign for the nomination."

"But while I will not be a candidate, I will not be silent. I intend to speak out clearly and forcefully, to influence as much as I can where we stand as a party and where we need to go as a nation," he said.

The decision will likely make the Democratic presidential nomination race mainly a two-person race between Clinton and Sen.

Bernie Sanders.

Even though Biden hadn't announced his bid, opinion polls have put him at third after Clinton and Sanders. Surveys have shown that Biden's absence in the race would be a boon for Clinton. (Yonhap)