LILLE, France — Two slumping political figures met in a symbolic embrace in Lille, France, on Saturday, but it was not clear whether the encounter would lift the faltering fortunes of either Stephen K. Bannon or Marine Le Pen.

Mr. Bannon, the former chief strategist for President Trump, was warmly applauded when he addressed the party congress of the anti-immigrant National Front, led by Ms. Le Pen. Striding angrily about the stage, he delivered a populist pep talk to a crowd still smarting from Ms. Le Pen’s crushing defeat in last year’s presidential election.

He was a surprise, last-minute guest, and his fiery speech, delivered in English through a sometimes faltering translator, stole the show from Ms. Le Pen.

A crowd that did not fill the auditorium rose to its feet, delighted that Mr. Bannon had attacked a political and economic establishment that has been the object of scorn and hatred in National Front doctrine for nearly 50 years.