About 649kg (1,430lbs) of cocaine was found hidden inside a vessel that had run ashore.
Police said the drugs were incinerated on Tuesday, apart from two packets, which have been sent to the US Drug Enforcement Administration for testing.
The drug haul has an estimated street value of $80m (£61m).
Drugs often wash ashore on the Marshall Islands, but last week's discovery set a new record.
The boat was found by a local resident on Ailuk atoll. Locals tried to move the vessel but were unable to due to its weight.
Upon further investigation, they discovered the packets of drugs in a hidden compartment inside the boat.
Marshall Islands Attorney General Richard Hickson said the boat could have been drifting for more than a year and was most likely from Central or South America.
In 2014, a man from El Salvador was discovered in a boat that had washed ashore on the island of Ebon Atoll. He said he had spent 13 months lost at sea and claimed to have survived by catching fish, birds and turtles with his bare hands.
After his rescue, researchers from the University of Hawaii conducted 16 computer simulations of drift patterns from the coast of Mexico and discovered that nearly all eventually ended up in the Marshall Islands.
Authorities in the Marshall Islands say the country has a drug problem caused by packets washing up on the shore, which are then sold on in the capital Majuro. Hospitals there have reported a rise in patients with complications relating to the consumption of crack cocaine.
Mr Hickson praised locals for notifying authorities about the most recent haul.