Ex-serviceman Roy Parkin is calling for the council to rethink its decision to fell 23 memorial trees on Western Road, Crookes.
The council claims the roots of the trees, planted in memory of Westways School pupils who lost their lives fin World War I, are damaging pavements.
Cabinet voted to fell them, claiming keeping them would have cost £500,000.
But Mr Parkin, whose placard features the regimental motto ‘Through mud and blood to green fields and beyond’, said: “I’m hoping if I carry on sitting here, they’ll turn round and say we’re not going to touch them.
“It’s about remembrance, you’ve got to remember the past and all the people who lost their lives.”
Passers-by have offered him food and drink, with one person buying him a bottle of water.
“I’ll keep coming down to the Town Hall and protesting until the council says there will be no more threats to Western Road memorial trees,” he added.
“It’s important to protest the tree felling because when I was growing up in the city centre, there weren’t any trees for square miles.”
“Children had to walk to the countryside if they wanted to play in the parks or green spaces.”
Mr Parkin, of Netherthorpe, who has lived in the city all his life, said: “The trees have made Sheffield a different place, a much better place to live.
“I’m proud that Sheffield is one of the greenest cities in the country, I just want it to stay that way.”
The council plans to replace the felled memorial trees at 36 sites across the city.