Carey Mulligan laughs. Then sighs, then laughs again.

The star of “Suffragette” is reacting to being told that, superimposed over a short online video she made on feminism, a pop-up ad reads “The No. 1 reason men pull away! The biggest mistake women make to kill a man’s attraction!”

“That’s so funny,” said Mulligan, who plays Maud Watts, a young working-class mother caught up in the women’s right-to-vote movement in 1920s London. “Especially when we’re talking about a film like this. I have to think of that kind of thing as white noise.”

Mulligan’s film career was auspiciously launched six years ago with the well-received 1960s coming-of-age tale “An Education.” Since then she has played Daisy Buchanan opposite Leonardo DiCaprio in “The Great Gatsby” and a folk singer married to Justin Timberlake in the Coen brothers’ “Inside Llewyn Davis.”

Maud, who must convincingly evolve from a nondescript laundry worker to a firebrand activist, could be her most challenging role to date.

“One big reason I was drawn to this project is that she’s a completely ordinary woman who finds a voice through these other women and becomes extraordinary,” she said. “So many stories are about people who already are extraordinary. This woman, you see her as she’s going through the process of being radicalized.”

“Suffragette” also features veteran actors including Meryl Streep and Helena Bonham Carter, but it’s really Mulligan’s picture to make or break. Did she feel that kind of pressure during shooting?

“No, it really felt like an ensemble to me,” she said. “Except when I was in a prison cell, alone.”

She recalls the suffrage movement as being little more than a footnote in history class, and learned a lot while making the movie about all the attempts to quell the women’s efforts that went on behind the scenes.

“I had no idea they were force-fed like that in prison; that was shocking,” she said. “And they only released the full private information on all the surveillance in 2003. The authorities felt threatened enough by these women to spy on them.”

Although she hails from a generation known for taking equal rights for granted, Mulligan said she’s “proud to be a feminist.” She was also tickled to work with Streep, who plays suffrage leader Emmeline Pankhurst.

“We only had two days together, but she blew everyone away,” Mulligan said.

“There was a buzz building up the day she was coming. Everyone was giddy. They turned the family room of the house we were shooting in into sort of a green room, and everyone was sitting on the sofa like little kids in kindergarten, with our faces in our hands, staring at her while she told stories. Kind of pathetic, but that’s just the way people feel about her.”

‘Just as relevant today’

Working on a film for which women took the lead behind and in front of the cameras was a thrill because it’s still rare, she said.

“Suffragette” screenwriter Abi Morgan (who also wrote the Margaret Thatcher biopic “Iron Lady,” for which Streep won one of her three best-actress Oscars) seconded that emotion.

“Working on it together made us all engage with our own feminism and activism more,” Morgan said. “So many of the issues raised in the film are just as relevant today — equal pay, sexual violence in the workplace, parental custodial rights.”

Morgan said she’s encouraged by “this generation of powerful young actresses who are standing up for themselves, but equality isn’t a nirvana state. The calibration is constantly changing.”

Noting that only 13 percent of screenwriters are women and only 9 percent are directors, she said, “Could this movie have been made five years ago? Yes, but it cost $14 million. I’m waiting for the day women are being given $100 million budgets.”

Below Mulligan’s short video online, a photo appears. It’s captioned “Carey Mulligan shows off her slender post-birth bod arriving at ‘The Late Show.’ ” (Mulligan and her husband, Marcus Mumford, frontman for the band Mumford and Sons, welcomed a baby girl, Evelyn, into the family several weeks ago.)

“White noise,” she said.