Marian Seldes, the Tony Award-winning actress who has played her share of divas since making her debut on Broadway 60 years ago, brings yet another one to the stage in Laurent Pelly’s new production of Donizetti’s comic “La Fille du Régiment,” which opens tonight at the Metropolitan Opera House. The arrogant, prickly Duchess de Krakenthorp is the sole speaking part in an opera that also boasts singing superstars Natalie Dessay and Juan Diego Flórez. The role, which puts Ms. Seldes onstage for no more than five minutes, marks the 79-year-old veteran’s debut in the 4,000-seat venue.

“Because of the enormity of the stage, you have a license to enlarge what you normally would do on a regular Broadway stage,” she said. “And that’s what the director kept urging me to do, so that it really fills the house.” Not that she’s ever had a problem projecting.

Ms. Seldes, who most recently appeared on Broadway last summer opposite Angela Lansbury in “Deuce,” was brought in as an emergency replacement for 74-year-old Tony winner Zoe Caldwell, who suddenly left the Met production a week and a half ago. “They made the costume faster that I could get the performance together,” Ms. Seldes said.

The tall and angular actress, who first appears in the second act, is decked out in a magnificent lavender gown — designed by Mr. Pelly and slightly old-fashioned, as he has updated the action to World War I — with an attention-grabbing hat atop her bouffant. The grande dame, part Lady Bracknell, part Wicked Witch of the West, has arrived at the castle of the Marquise of Berkenfield to work out marriage arrangements between her nephew and Marie, the opera’s title character. As the orchestra plays an innocuous minuet, Ms. Seldes, with cane, does a little dance with comic gesticulations. Impatient and imperious, she ultimately hums along with the orchestra, expressing discontent with the conductor’s tempo. You know who’s boss.

“The physical life of the character is so desperately important,” Ms. Seldes said. “Although I didn’t become a dancer, I kept studying to be a dancer. I don’t regret a minute of it.”

Aside from knowing how to draw with her body, what Ms. Seldes does best is deliver a line, and Mr. Pelly’s rewrites of the libretto have made some of the comedy snappier. When the Duchess asks the Marquise if she’s found a caterer for the wedding, she adds, “And remember, sweetheart, don’t be stingy with Veuve Clicquot!”

The operatic dimension of Ms. Seldes’s dramatic style outside the Met has served her well. “But I have to be careful about that because that era is over,” she said thoughtfully, “and it can be a criticism, not a compliment. Sometimes I have to pull back.” On the Met stage, she doesn’t.

“I’ll tell you something odd,” Ms. Seldes said. “The first time I was ever on a New York professional stage was October 12, 1942, at the old Metropolitan Opera House. It was a celebration of Michel Fokine, the great choreographer. He had died that summer and I was a student at the School of American Ballet, and I was in the crowd scene in ‘Petrushka.’ So it’s my second Metropolitan Opera debut in both fields in which I’m not expert at. I was never a ballerina and I’m not a singer.”

But without high C’s or high kicks, Ms. Seldes manages always to sing and dance her lines, ever since winning her Tony in 1967 in Edward Albee’s “A Delicate Balance.” “I just don’t want to be on the stage and act,” she said. “I want to interpret as closely as I can what the author wanted. That’s my mantra.”

A longtime music lover, Ms. Seldes said, “Opera’s the quintessence of theater — dance, music, and acting. As an audience, I can give myself to it completely. I never feel critical when I’m in an opera house. Give it to me, I want it.”