"From his historic announcement in support of marriage equality to his ongoing commitment to achieving full federal equality for LGBT Americans, the Vice President has proven time and again that he’s a stalwart ally to our community, and we’re honored he’ll be joining us to deliver the keynote address at the HRC National Dinner," Chad Griffin, president of the Human Rights Campaign, said in a statement.
The Human Rights Campaign had previously announced Clinton as a major speaker at the event, earlier in the day before about 800 guests. Late this week Biden's prime-time appearance was locked down, and he will speak before more than 3,000 guests.
The vice president's advisers have declined to specify when he will announce his decision to run for the Democratic nomination, but some feel that he must make the call by early next month in order to gather enough resources to finance the effort to ensure Biden gets on the ballot in all the states.
The gay rights group has not endorsed any candidate for president and is likely to await decisions by Biden and any other Democrats still considering a bid.
The movement toward the recent Supreme Court ruling declaring a right to marriage for gay couples received a jolt more than three years ago when Biden unexpectedly declared his support for same-sex marriages during a 2012 interview, ahead of President Obama and Clinton.
Clinton took months longer to make her own declaration in support of marriage rights for gay couples.
The former first lady and U.S. senator has raised tens of millions of dollars for her presidential campaign, while she continues to hold sizable leads over a potential rival, Biden, and actual contenders, Sen. Bernie Sanders (I-Vt-.). The vice present has taken none of those steps, and even some friends believe that his lingering doubt following his son's death has left Biden with not enough room to collect his grief and move on.
A decision from Biden is expected in early October, although some advisers have quietly wondered whether they could await several big events for Clinton next month and then determine whether he could make a very late move into the race.