The space rock, which is called 1998 QE2, is so large that it is orbited by its own moon
It made its closest approach to our planet at 20:59 GMT (21:59 BST), but scientists had said there would be no chance it would hit.
Instead it kept a safe distance – at closest, about 5,800,000 km (3,600,000 miles).
Prof Alan Fitzsimmons, an astronomer at Queen’s University Belfast, said: “It’s a big one. And there are very few of these objects known – there are probably only about 600 or so of this size or larger in near- Earth space.
“And importantly, if something this size did hit us one day in the future, it is extremely likely it would cause global environmental devastation, so it is important to try and understand these objects.”
This fly-by gave astronomers the chance to study the rocky mass in detail.
Using radar telescopes, they were due to record a series of high-resolution images.
They want to find out what it is made of, and exactly where in the Solar System it came from.
Prof Fitzsimmons said: “We already know from the radar measurements, coupled with its brightness, that it appears to be a relatively dark asteroid – that it’s come from the outer part of the asteroid belt.”