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President Obama will formally inaugurate Organizing for Action, his newly-formed independent advocacy group, with a headline speech Wednesday night before the group's Founders' Summit in Washington.

Obama's appearance, confirmed to ABC News by an OFA official, will be his first in-person with the group's core team of advisers, donors and grassroots organizers since its formation following the 2012 election.

It comes as Obama seeks to re-energize his expansive grassroots campaign infrastructure around top second-term priorities - from new gun-control measures to comprehensive immigration reform and a plan to replace sequester - and cement the foundation for his presidential legacy.

The summit will stretch over two days at Washington's St. Regis Hotel, including a series of meetings, discussions and brainstorming sessions aimed at shaping the group's advocacy agenda and grassroots mobilization strategy, the official said. It will also engage key Democratic donors who have pledged to underwrite the group.

Obama has drawn criticism from government watchdog groups and some Republicans for reportedly promising regular face-time at quarterly meetings to wealthy would-be donors - a charge which OFA has denied. He is not expected to spend any one-on-one time with the donors in attendance on Wednesday, the official said.

"Everyone will be in one room," including donors, former campaign aides and dozens of grassroots organizers and volunteers, the official told ABC News. The group has pledged to voluntarily disclose the identities of its donors and post online the amounts of their contributions.

Also attending the gathering are former Obama campaign manager Jim Messina; senior adviser David Plouffe; OFA executive director Jon Carson; outgoing EPA administrator Lisa Jackson; and other prominent organizers, according to the OFA official.

Obama's planned speech at the OFA Founders' Summit was first reported by Politico.