The headquarters of South Oxfordshire and Vale of White Horse district councils in Crowmarsh Gifford were gutted on 15 January last year.
About 400 staff have been working from home or at temporary sites ever since.
Now, exactly one year on, the councils have confirmed they are looking for a new building on a new site.
Andrew Main, 47, from Rokemarsh, admitted starting the fire and has been detained in a mental health unit.
A spokesperson for both councils said: "Whilst no formal decisions have been made, it's likely we won't be returning to Crowmarsh.
"We're focusing on finding a new building on a new site that's fit for purpose and gives the best value for money for our council tax payers.
"We're actively looking at the options for our permanent home and we hope to have a final decision in the next few months."
Both councils are temporarily based at Milton Park in Abingdon after signing a four-year lease.
The estimated cost to the councils of repairing the damage to their offices was put at about Â£20m.
Two councils forced to move after their offices were devastated by a rampaging arsonist will probably never return to their former home, a spokesperson said.