The London plane tree has stood in the city's Centenary Square since the 1930s, making it one of the oldest in the heavily redeveloped city centre.
But the city council now says it will be removed as part of a £10m revamp of the square, allowing it to be used for public events without fear of it being targeted by recent Nice- and Berlin-style attacks.
This will involve strategically siting heavy stone benches which will double as barricades to keep vehicles out.
Birmingham City Council deputy leader Ian Ward said: "These benches need deep foundations and this will unfortunately mean the tree roots being cut. We looked at moving the bench forward, but we need the space in the square for big events."
The plane is just one of 25 trees due to be felled as part of the work, though 59 replacement trees will be planted, which "will be more than acceptable to compensate", Ward added.
Nearly 1,600 people have already signed an online petition to save the tree.