Brent Renaud, an American filmmaker killed in Ukraine, captured the human toll of war.

When Brent Renaud, an award-winning American filmmaker and journalist, was killed in Ukraine on Sunday, he was there to do what he had done throughout his career: bear witness to the world’s most dangerous stories.

At the time of his death Mr. Renaud was on assignment for Time Studios working on a “project focused on the global refugee crisis,” according to a statement from Time executives.

Through his extensive film catalog, Mr. Renaud highlighted the human impact of war and conflict, said Vivian Schiller, who commissioned Mr. Renaud’s 2004 documentary series about the Iraq war for The New York Times and Discovery Channel.

“He was just a filmmaker with tremendous heart,” Ms. Schiller said on Sunday. “It really sort of pervaded all of his work.”

Mr. Renaud, 50, often collaborated with his brother, Craig, to produce film and television projects for The Times, HBO, NBC, Vice Media and other companies. He filmed in conflict zones and risky areas, including parts of Afghanistan, Haiti, Iraq, Mexico and Ukraine.

One of his earliest projects was “Off to War,” an intimate 2004 documentary series he created with his brother. Over six months in Arkansas and then a year in Iraq, the brothers followed a group of Arkansas National Guardsmen from the training ground to the battlefields.

The series was personal for the brothers because they too were from Arkansas. The film focused as much on the families ripped apart by war as it did on combat struggles. At one point, after multiple soldiers had died, a unit leader suggested that the brothers go home, Mr. Renaud said in a 2009 interview with Curator Magazine.

“It wasn’t a consideration for us — the danger was not an issue, and the story was not complete,” he said.

The series marked the start of Mr. Renaud’s intrepid, globe-trotting career. He and his brother took their cameras around the world, from Black Lives Matter protests in Little Rock, Ark., to the 2008 Beijing Paralympic Games.

In a 2015 documentary for The Times, Mr. Renaud scaled barbed wire fences and waded through rivers to film child migrants fleeing Central America for the United States.

The brothers survived several near-death situations, including car crashes, blasts from improvised explosive devices and attacks from members of the Egyptian military, they said in a 2013 interview with Filmmaker Magazine.

The Renauds learned to travel with little equipment, sometimes only using a cellphone camera if they needed to be discreet, they said. Shortly after Mr. Renaud finished college, he said he traveled to Cambodia with a small camera that he “barely knew how to use.”

“I somehow managed to be taken seriously and landed an interview with one of the top operational generals of the co-prime minister,” he said.

The brothers won multiple awards, including a 2012 duPont-Columbia University Award for the 11-minute film “Surviving Haiti’s Earthquake: Children,” and a 2014 Peabody Award for “Last Chance High,” a series about Chicago students with emotional disorders.

Mr. Renaud was a fellow at the Nieman Foundation for Journalism at Harvard University from 2018 to 2019.

Mr. Renaud’s final assignment on Sunday was capturing refugees fleeing across bridges in Irpin, according to his reporting partner, Juan Arredondo, who described the events in a video posted on the Okhmatdyt hospital’s Instagram page. As always, he was trying to capture the human toll of a geopolitical conflict.

“We don’t seek out the dangerous assignments,” Mr. Renaud told Curator Magazine in 2009. “But once we are committed to a story, we are willing to do whatever it takes to tell that story.”