Two cities told to lose 26 councillors by the High Court are to hold elections to replace 25 of them on 9 September.
Councillors in Exeter and Norwich were ordered to go after being allowed to stay in office as part of preparations for becoming unitary authorities.
The High Court overturned their permission to become unitary councils and take over county council services.
Exeter is to hold polls in 12 wards after one councillor was allowed to stay. Norwich is to hold 13.
Exeter and Norwich city councils were granted unitary status by the previous Labour government in February.
The fired councillors were due to stand for re-election in May but had been granted extensions in office as part of provisional arrangements to implement the new status, which was due to begin in 2011.
The Conservatives vowed before the election to overturn the decision to allow the splits, saying they were a waste of money. The High Court backed the revoking of the status in June.
The unitary status meant the cities would have taken over social services, schools and roads from their respective county councils.
Earlier this month, the High Court ruled the by-elections must take place to maintain legality.
Although Exeter was told to replace the 13 councillors, Tim Payne was only elected to the Pennsylvania ward in May for a four-year term.
The court had since agreed he could remain in office, Exeter City Council said.