Each pill sold for $50, Sgt Collin said.
Singleton, who was released on bail following his arrest the next day, admitted charges of possessing ecstasy for supply and supplying ecstasy.
Each carries a maximum penalty of 14 years' imprisonment.
Lawyer Michael Walker said the defendant, who is on a work visa and employed by an electrical firm — knew he had made a "grave mistake and is aware of the consequences of that mistake".
Judge Farnan told Singleton he "may have been somewhat naive".
"You didn't appreciate the significance of your offending, and the seriousness of it."
Judge Farnan remanded him on bail for sentencing on March 15. Bail conditions include not to contact his partner, a nightly curfew and a ban on entering licensed premises, except for supermarkets.
The conviction comes a week after Detective Senior Sergeant Malcolm Inglis, of Queenstown, said the resort was New Zealand's capital for ecstasy, also known as MDMA.
Det Snr Sgt Inglis said officers had been targeting ecstasy dealers this year after wastewater testing showed the Southern police district, which includes Otago and Southland, was the worst in the country for the drug.
They were also concerned that other chemicals were being sold under the guise of ecstasy and officers had had to call ambulances on nights out because of people having life-threatening reactions.