The company's flagship Agera RS clocked an average 447.2km/h during two timed runs on a 17km section of a highway just outside Las Vegas last weekend, eclipsing the Bugatti Veyron's becnchmark of 431.1km/h set in 2010.
Per the standard format for setting a land speed record, Lilja made two runs in opposite directions within the space of an hour to eliminate the effects of gradients and wind, with the two recorded speeds then averaged.
This very same vehicle was stretched to its Earth-scorching limits by factory test driver Niklas Lilja on Saturday, along an 11-mile (17.7 km) piece of public highway near Las Vegas on Saturday that had been shut down by Nevada authorities for the attempt.
The Agera RS used in the attempt is the same one that recently set a time of 37.28 seconds for the 0-250-0 miles per hour run.
On its first run, the £1.5 million Agera RS hit 271.1mph, reaching 284.7mph on its second run. After recently toppling Bugatti's impressive zero to 249 miles per hour to zero record, the team tackled the overall top speed record in Nevada.
The previous record was the 267.8 miles per hour set by the Bugatti Veyron Super Sport in 2010. It is powered by a 5.0-litre twin-turbo V8 that produces 865kW and upto 1280Nm of torque and just 25 of the hand-built Swedish machines will be built.
Koenigsegg also claims to have set another record on the day. On one run Lilja reached 271.2 miles per hour, and on the other he reached 284.6 miles per hour.
Special mention should be made regarding the tires the Agera RS was running.
The Swedish hypercar firm confirmed on Twitter earlier today that the Agera's factory-fitted Michelin Pilot Sport Cup 2s were used for the run, but other than that, we don't know a huge amount about the feat - full details are expected to be revealed soon.