Ulster Unionist Derek Hussey was disqualified after an investigation by the standards watchdog last July.
Andy McKane was selected by the party to take over Mr Hussey’s seat.
Mr Hussey has three convictions for drink-driving offences and was banned from driving for five years in 2016.
The Electoral Office has said it was notified on Wednesday that Mr Hussey has been co-opted to fill the seat again, with effect from November 1.
An Ulster Unionist spokesperson said the former deputy mayor had been co-opted to council following Mr McKane’s decision to step aside.
“In July 2019 councillor Hussey was disqualified from council for 15 months for previous drink drive convictions,” the spokesperson said.
“He has apologised profusely and continues to express remorse for his actions.”
The spokesperson said Mr Hussey “will focus on doing his best to represent all the people of the Derg District Electoral Area”.
Mr McKane told BBC News NI he was legally entitled to remain a councillor until the next election but that stepping aside was the “honourable thing” to do.
“I am conscious that I was not elected to the seat and it may be the opinion of some that I took something that wasn’t mine,” he said.
“Therefore I feel the honourable thing to do is to step aside and maintain my integrity, which I see as vital when acting as a public representative.”
At the time of Mr Hussey’s disqualification, some families criticised the decision and said he should have faced tougher sanctions.