Pete Reed, 33, was killed on Thursday in the city of Bakhmut. He was a Marine veteran from Bordentown, Burlington County.
Reed was the Ukraine country director for Global Outreach Doctors.
The organization said Reed was helping to evacuate Ukrainian civilians when his vehicle was hit by a reported missile.
"He died doing what he was great at, what gave him life, and what he loved, and apparently by saving a team member with his own body," according to a Facebook post from his family.
Global Outreach Doctors said the team is devastated by the news.
"Pete was a beacon of humanitarian work - an incredible visionary, leader, compassionate care provider, and an inspiration to us all," the organization said in a statement.
"He selflessly dedicated his life in service to others, especially those affected by disaster and war. Pete accomplished more in his 33 years than most of us in our entire lives," the statement continued. "He leaves behind an incredible legacy."