Alexander Scott Hagan was set to fight allegations he helped traffic drugs from the ACT between June and October in 2014 during an ACT Supreme Court trial next week.

But Hagan, 52, instead pleaded guilty to three drug trafficking charges related to cocaine, MDMA, and a large commercial quantity of methylamphetamine, before Justice John Burns on Friday.

Crown prosecutor Shane Drumgold told the court both parties still needed to settle on an agreed statement of facts, but the three charges took in all the drug trafficking outlined in the documents.

In a statement issued at the time, ACT Policing said officers seized the drugs from the boot and body work of the car when they searched a Volkswagen Passat after watching a man leave a Curtin about 1.30pm on October 23, 2014.

Police later alleged in the ACT Magistrates Court that Hagan had been involved in the transporting and trafficking of the drugs from Canberra to another location.

ACT Policing said the seizure was the result of a long-standing investigation, Operation Davos, which targeted an interstate drug syndicate involving cocaine.

Detective Sergeant Shane Scott said at the time that the drug haul - which police claimed was the biggest in the territory's history - was likely destined for the Victorian illicit drug market.

"This amount of drugs could equate to 280,000 street deals valued at over 25 million dollars."

Justice Burns ordered a pre-sentence report be prepared before Hagan is sentenced in August.