Ulster Unionist Derek Hussey, a former deputy mayor in the council, has three convictions for drink-driving offences.
His solicitor said he will appeal the decision made by the Local Government Commissioner for Standards.
Mr Hussey was previously chair of the Policing and Community Safety Partnership (PCSP).
The disqualification begins at noon on 16 July.
A spokesperson for the UUP said: “We have always been of the view that drink driving is unacceptable and the decision today reflects that view.
“We will be taking steps to ensure that the people of Derg are well represented in Alderman Hussey’s absence and will make no further comment at this time.”
Mr Hussey was first elected as a councillor in 1989, and re-elected to his seat in the local government elections earlier this year.
The hearing was told that Mr Hussey had drink driving convictions from 2004 and 2011, and then again in March 2016, relating to offences the previous year.
In the most recent incident in 2015, Mr Hussey’s vehicle struck another, causing injury to the other driver.
Mr Hussey was later arrested and breathalysed at his home – the level of alcohol in his blood was more than twice the legal limit.
He was also convicted of leaving the scene of the accident, and failing to report it.
He was fined £800 and ordered to complete 100 hours of community service, and banned from driving for five years.
The conduct hearing has taken place because of the complaints of two members of the public.
These included those who had lost relatives to drink drivers and felt that the councillor should not be in a position of public responsibility.
They alleged that Mr Hussey had broken the Northern Ireland Local Government Code of Conduct for Councillors.
During the hearing, it was revealed that Mr Hussey accepted that he had broken paragraph 4.2 of the code, because his actions had brought a councillor and the council into disrepute.
Arguing for disqualification, the Deputy Commissioner, Paul McFadden, pointed to what he called Mr Hussey’s “repeat offending”.
He told the hearing that “the bar cannot be so high that someone must die before drink driving is taken seriously”.
Mr Hussey’s solicitor said his client strenuously denied any lack of insight into the seriousness of his actions.
He questioned the level of disrepute into which his client and the council had been brought.
He also pointed to the positive cross-party character references provided for his client.
After the evidence was heard, it fell to the acting commissioner for standards, Ian Gordon, to decide on the level of sanction for Mr Hussey.
Disqualifying Mr Hussey from being a councillor for a period of 15 months, he said he was “not persuaded that the respondent had demonstrated sufficient insight into the seriousness of his actions”.
Depending on the outcome of any appeal, Mr Hussey may have to be replaced on Derry City and Strabane District Council.
His party would have to co-opt a replacement.
A relative of one of the complainants said his family was “very happy” with the decision by the acting commissioner.