Associated Press photographer Burhan Ozbilici was at the launch of a new art exhibition in Ankara on December 19 when Mevlut Mert Altintas, an off-duty police officer, opened fire and killed Andrey Karlov.
It was "an explosive image that really spoke to the hatred of our times," Mary F. Calvert, a member of the World Press Photo jury, said in a statement.
"Every time it came on the screen you almost had to move back because it's such an explosive image and we really felt that it epitomizes the definition of what the World Press Photo of the Year is and means."
Jury member Tanya Habjouqa added: "I think we were brave in our decision. We were bold. I think the selection is definitely going to push forward a debate and I think it is a debate that is essential to have."
Karlov, envoy to Turkey since 2013, was invited to give a speech at the exhibition in Ankara, which featured the work of Turkish photographers in the Russian countryside.
The longtime diplomat had begun to speak when Altintas, wearing a dark suit and tie, fired shots in rapid succession, according to multiple witness accounts.
The ambassador fell to the floor. The gunman circled his body, shouting "Do not forget Aleppo!" and smashing photos hanging on the wall.
Speaking to CNN in December
, Ozbilici recalled the moment the assassin opened fire. "I heard shots, very loud -- bam bam bam," he said.
"The people standing in front they disappeared. They threw them(selves) on the floor. They were trying to hide, to take shelter. I was shocked ... afraid ... not panicked.
"In difficult situations, I'm calm. I have a responsibility to record the event," he told CNN.
Within just a few minutes, Ozbilici's photographs were seen by people across the globe. He was widely praised for his composure and courage during the incident.
Ozbilici's photo was chosen as the winner from over 80,000 entries by a jury of internationally-recognized photojournalists and photographers. The award carries a prize of 10,000 euros.