"He was driving an Auckland Co-op Taxi which had the roof light illuminated saying 'for hire' and his logbook had not been signed off as having finished," court documents said.
"In explanation the defendant stated he had one Kingfisher beer and was heading home."
At Manukau District Court, Singh was recently fined $1000 and stripped of his licence indefinitely.
Auckland Co-op Taxis chairman Jacob Patel said public safety was paramount and the incident had prompted the company to take rapid action.
"You can't dismiss anybody without proper rules so very quickly I put it to the board and we made a resolution - anybody convicted will never ever be taken back," he said.
"Anyone caught drinking and driving, whether he has got his permit back or not, he will never ever be able to drive for Co-op."
Singh was not the first driver to be sacked by the company for drink driving.
Mr Patel said he had earlier found out about another couple of drivers who had racked up convictions - it was unclear whether they were on duty at the time - and they too would never work for the company again.
Once Singh has been disqualified for more than a year, the New Zealand Transport Agency (NZTA) will decide whether he is fit to hold a licence again.
He will have to convince them he has tackled any alcohol problems before his licence is reinstated.
In 1999, NZTA set up a system called "Driver Check" which allows employers to be notified when staff members' licences change.
Spokesman Andy Knackstedt said if a taxi driver was charged with a criminal offence police notified the agency which would suspend the defendant's P (passenger) licence, creating an alert in the system so bosses were aware.
About 1300 employers are currently signed up to the service.
