The hypercar was driven on two runs in opposite directions of an 11-mile stretch of closed public highway between Las Vegas and Pahrump.
The Agera RS clocked an average speed of 277.9mph over the two runs, easily beating the 2010 record of 267.8mph that was set by a Bugatti Veyron Super Sport. That car's aerodynamic features, including a huge rear wing, creating too much drag to be suitable for a record setting top-speed run though. Towards the end of the second run, the Agera RS even surpasses 450 km/h - close to the speed of a small aircraft.
Bugatti is expected to attempt an official top speed record with its Chiron in the near future, using a new tyre design from Michelin.
Just last month, the auto was also in the record books after Lilja drove from a standstill to 249mph and back to a full stop in just over 36 seconds - beating the Bugatti Chiron's 41.96-second time that had been set by former F1 driver Juan-Pablo Montoya.
In claiming the production vehicle land speed record over the weekend, Koenigsegg left previous record-holder Bugatti, which claimed the throne with a 268-mph (431-km/h) effort in 2010, in its wake.
With a 5.0-litre twin-turbo V8 producing an eye-watering 1,380bhp, the Agera RS can accelerate from 0-249mph and back to 0 in just 36.44 seconds. That includes the Bugatti Veyron Super Sport, which has held the official record of 267.8 miles per hour since 2013. Responsible for sending the power to the pavement was reportedly a set of Michelin Pilot Sport Cup2 tires - the standard tire for the Agera - which seemed to survive the high-speed stint without a hitch. This is not the first time that Koenigsegg broke a world record held by Bugatti, as it happened just last month.