CANNES, France -- Jeff Nichols, sitting calmly by the beach, was surprised to notice a curious lack of butterflies amid the usually anxiety-ridden premiere experience at the Cannes Film Festival. His film, "Loving," is about Richard and Mildred Loving, the Virginia couple whose biracial marriage in 1958 led to a landmark Supreme Court decision on marriage equality.

"It's not my story," said the writer-director, whose previous films, including the Mississippi River coming-of-age tale "Mud" and the science-fiction thriller "Midnight Special" were original creations. "It's their story."

"Loving," starring Joel Edgerton and Ruth Negga, is told straightforwardly and simply. Although it has the context of a civil rights drama, it's a portrait of a humble, unassuming love so steadfast that it eventually toppled one of the most odious legal remnants of slavery-era America -- the ban against interracial marriages.

Without the standard Hollywood histrionics, the film patiently accumulates considerable force before finally overwhelming the viewer.

"No one moment adds up to the whole. But if you put them all together, hopefully, the weight of it gains this emotional density," said Nichols. "Part of the cruelty of what was happening to them was time. Time was being taken away from them."

The Lovings didn't seek the spotlight, but their efforts to return home after being exiled from Virginia eventually led to the 1967 Supreme Court ruling of Loving vs. Virginia -- a decision cited in the court's 2015 ruling on same-sex marriage.

Nichols and Edgerton believe the film has obvious significance at time when religious liberty laws and restroom battles are being fought in the U.S.

"It's kind of shameful to watch and look back and think 50 years ago that that was happening and yet it's still very much relevant today," says Edgerton. "Things are changing, obviously, but it's weird to think we'll look back in 20, 30 years' time and say that law (gay marriage) changed in 2015."

Of the many films in Cannes, "Loving," which Focus Features will release in the heart of awards season in November, is among the most likely to garner significant attention from both moviegoers and the Academy Awards. The performances of Negga and Edgerton have already been widely hailed.

"This is the most important film I've made and it's one of the most important films in history, I think," Negga told reporters in Cannes. The Irish-Ethiopian actress -- the first Nichols auditioned for the role -- pursued the part fervently. "There was no alternative, really. I just really had to play her."

Both actors drew from the famous images of the couple , who were photographed by Life magazine's Grey Villet (Michael Shannon in the film) in 1966. The photographs captured their sweet, almost teenage-like manner together. In one, Richard -- a buzz-cut blond country boy -- lies with his head in Mildred's lap while watching TV.

Nancy Buirski's 2011 documentary "The Loving Story" was also a major inspiration.

"The court case is fascinating, but I just wanted to hang out in that documentary footage more," says Nichols. "I wanted to go around the edges of it. I wanted to go around the corner of it."

Avoiding inflated dramatics, Nichols and his cast sought to stay true to the Lovings, who effected change just by being.

"To me, it's like this series of checkmates. It tends to move and be shut down. Move and be shut down. Have a voice and be stifled," says Edgerton. "Finally when the Supreme Court decision releases that weight, it's quite an overwhelming feeling. It's a triumphant feeling, but when Richard proposed in the field that should have been their right and freedom at that time."

Richard Loving died in 1975, the victim of a drunk driver, and Mildred Loving died in 2008.

"Loving" may be a departure for Nichols in that it's a true-life tale. But it continues the Arkansas-native's interest in the preservation of family amid elements out of one's control.

Choosing to make the film, though, was easy enough. When he first shared the trailer of "The Loving Story" with his wife, she told him if he didn't make it, she'd divorce him.

"That's all she wrote. She didn't sign off or anything," recalled Nichols, chuckling.