Family members of Hamza "Travis" Nagdy, 21, confirmed him as the victim to the Louisville Courier-Journal in the shooting which took place at 12.30am on Monday.
Louisville police did not provide more details and no suspects have been identified.
In a social media post on Monday, Mr Nagdy’s mother, Christine Muineach, said her “beautiful and intelligent son” had been killed in a carjacking.
Mr Nagdy was among hundreds of protesters who took to the streets of Louisville over the summer to demand justice for Breonna Taylor, a 26-year-old Black woman who was shot dead by police during a bungled drugs raid on her home in March. No drugs were found at the property.
Her death, and the killing of George Floyd in Minneapolis two months later, led to nationwide protests over police brutality against minority communities.
Mr Nagdy was a key organiser in those Black Lives Matter protests in Louisville and was often seen leading chants and marches. On Monday a few dozen people gathered at the spot where Mr Nagdy was killed.
Some in attendance wore T-shirts bearing Mr Nagdy’s face and chanted "there ain't no justice in this town".
At least 200 people gathered at Jefferson Square, scene of many earlier protests, later in the evening to sing Mr Nagdy's name and recite his favourite chants, according to the Louisville Courier-Journal.
"I hope he will be a symbol of this violence and that we'll finally say, 'This stops with Travis,'" Antonio T-Made Taylor, an independent reporter who mentored Mr Nagdy, told LCJ.
"He's irreplaceable. Travis really believed he could help change systemic racism. He believed he could be a big part of that change," he added.
Louisville Metro Police spokesman Matt Sanders said the victim was rushed to the University of Louisville Hospital where he died of his injuries.
LMPD's homicide unit is investigating the killing.