Shortly after filming a pivotal scene in his new film, “A Single Man,” British actor Colin Firth learned a painful lesson. In the scene, Firth’s character, the gay college professor George Falconer, receives a late-night phone call. The voice on the other end of the line says that George’s longtime lover, Jim, has died in a car accident.

And George, for reasons particular to the bigotry of American society in 1962, is not invited to the funeral. In that instant, George’s heart sinks, tears begin to well and the world seems to collapse around him.

On the very day the scene was shot, Firth said in a recent phone interview from his home in London, voters in California narrowly passed Proposition 8, a resolution that prohibits same-sex marriage. It was a crushing defeat for gay rights supporters, which had the unexpected effect of lending this highly stylized period film a sense of modern urgency and relevance.

Indeed, since the film debuted at the Toronto Film Festival in September, it has been steadily gathering accolades from critics and audiences the world over. Firth’s performance, a nuanced balance of confidence and vulnerability at which the actor excels, is the subject of mounting Oscar buzz. The film opened locally on Friday.

“It would be very easy to consign that to the follies of the early ‘60s,” Firth said of the jarring scene, “if it hadn’t been for the fact that a law got passed in what we perceived to be an extremely progressive state in the United States, which was one of the most retrograde and bigoted pieces of legislation you could imagine.”

Firth considers the film an important statement against the stigma that surrounds gay relationships to this day.

“There are forces which I think are extremely negative and inhumane out there,” Firth said of the interest groups behind the passage of Proposition 8. “Having said that, I think a film like this can overcome it. I think it overcomes it by being unassumingly frank about homosexuality as being perfectly mainstream in the world in which this is framed.”

In addition to Firth’s performance, the film has grabbed the attention of critics and moviegoers for being the surprisingly assured directorial debut of fashion designer Tom Ford.

In 2004, Ford left Gucci, the Italian fashion house he transformed into a multibillion-dollar enterprise, and turned his attention to filmmaking. He decided to make “A Single Man” after rereading the slim 1964 novel by Christopher Isherwood upon which the film is based. After years of scrutinizing Firth’s screen performances, Ford approached the debonair actor about taking on the role. The pitch came out of left field, Firth said, but the unusual nature of the project immediately intrigued him.

“This didn’t speak of a vanity project or the fashion world or the catwalk. This was about a lonely gay college professor in 1962,” Firth said. “I thought, ‘This is not what I’m expecting in any way.’ I didn’t expect to hear from Tom Ford, for a start. I didn’t expect Tom Ford to be making a movie. I didn’t expect him to approach me if he were to make a movie, and I didn’t expect him to do something which sounded so personal.

“I’m lucky enough to have consistently been employed, so I’m usually not afraid of being out of work,” Firth said. “But I might sometimes be afraid of getting bored.”

Firth praised Ford’s approach as a director, which he said was as meticulous as his polished public persona would imply, but also allowed the film’s principal cast — Julianne Moore, Matthew Goode, Nicholas Hoult and Firth — plenty of freedom.

“You can see perfect composition. You can see the perfect judgment when he introduces a music cue, if you’re paying attention, you can. You can see little, tiny, almost inconspicuous jump-cuts. You can see his control of the editing,” Firth said. “But at the same time, you see an awful lot of free space, a lot of shots that just play out, where actors are just left to do what they do, where natural light is allowed to just exist, where he’s not using insecure, cheap narrative effects to try to kind of wrap things up. He’s allowing it to be what it is.”

Firth revealed a perplexing modesty about his looks — and those of the other actors in the film — in saying that Ford “didn’t pick people who looked like the cover of fashion magazines.”

“I’m not saying he picked unattractive people. . . I mean, he made us all look the best we could possibly look, but we are not, you know, designer models, none of us,” Firth said. “I can look pretty bloody awful, I can tell you. It was Tom’s talent that kind of flattered me and all of us.”

Firth’s legion of fans, whom he has consistently charmed and disarmed with his particularly British brand of well-mannered masculinity for nearly 30 years, might disagree. Firth’s appeal as a leading man was cemented in the BBC television miniseries “Pride and Prejudice” and continued in such popular successes as “Bridget Jones’s Diary,” “Love, Actually” and “Mamma Mia.”

But Firth’s gifts, as he is out to prove in “A Single Man,” have long extended far beyond the realm of the feel-good chick flick. His first screen appearance, opposite Rupert Everett in the 1984 adaptation of Julian Mitchell’s “Another Country,” marked the debut of a serious actor with serious aspirations. Since that debut, Firth has resisted typecasting by appearing in films as diverse as “Apartment Zero,” “The English Patient,” “The Importance of Being Earnest,” “Shakespeare in Love” and “Girl with a Pearl Earring,” in which he played the Dutch painter Johannes Vermeer.

The opportunity to play George provided a new challenge for Firth, who will turn 50 in September, but, he suggested, it had far more to do with the character’s journey of loss and redemption than with his sexuality. “You don’t have to be gay to be gay [on film],” Firth said. “This is just a mainstream thing. This is just love.”