It is understood Michael O’Neill, 47, was helping those caught up in the conflict against Russia when he was killed last week.
Bernadette Doyle said her brother, who was a truck driver, joined a humanitarian organisation in March 2022 because he saw a desperate need for help in Ukraine.
“He knew it was dangerous but could see that outside help was desperately needed to assist conveying women and children to safer places,” she said in a statement.
“[Michael] became more involved delivering supplies onto the front lines, assisting with the retrieval of the injured and deceased”.
According to Ms Doyle, this exposed the father-of-three to increased danger.
Michael O’Neill grew up in the Huon Valley in Southern Tasmania and has been remembered as a keen sportsman and talented Australian Rules footballer.
Mr O’Neill and his brothers played for the Kermandie Football Club, which folded in 2010.
On Sunday, the Southern Storm Under 17 girls team took to the Kermandie Oval wearing the old Kermandie Football Club jumper in his honour.
The O’Neill family still has a strong connection with the southern Tasmanian football club.
“There’s a few O’Neill girls running around today,” Mr Synnott said
“Obviously, it’s tough on everyone, and as is always the case, people are working through it”.