The New Republic will celebrate its 100th birthday on Wednesday with a black-tie gala in Washington featuring remarks by Bill Clinton and Ruth Bader Ginsburg, a performance by Wynton Marsalis and a 400-person guest list studded with boldface names.

For those in an extra-nostalgic mood, the party has brought to mind the magazine’s semilegendary 70th-anniversary gathering in 1984, when Barney Frank and Gary Hart mingled with Henry A. Kissinger, who in an after-dinner speech declared it “traumatic” to be photographed with so many liberals.

“The pictures are kind of a scream,” said Franklin Foer, the magazine’s 40-year-old editor, vicariously reminiscing about the days when The New Republic was toasting its status as the hot political magazine of the moment. “You look at them and then at Washington now, and you think, ‘Wow, that’s quite a tumble.' ”

Like Washington’s cast of characters, The New Republic has also changed. Under Chris Hughes, the Facebook multimillionaire who bought the magazine in 2012 from a consortium including its longtime owner Martin Peretz, the biweekly publication has more than doubled its staff, redesigned its print edition and broadened its coverage to be less Beltway-centric. It has also vastly increased its web traffic to more than four million unique users a month, according to the magazine.

And further changes are afoot. As the anniversary arrives, Mr. Hughes has hired Guy Vidra, a 40-year-old former Yahoo News executive, for the top of masthead as The New Republic’s first chief executive. This has set off speculation in Washington journalism circles that a magazine as famous for its ferocious office politics as for its contrarian political coverage might be on the verge of another round of upheaval...