Blasting off on an Ariane 5 rocket from Europe’s Spaceport in French Guiana, the device will take the title of the largest and most powerful telescope ever sent into space.
It follows the Hubble Space Telescope as the next great space science observatory, designed to answer questions about the universe and to make breakthrough discoveries in all fields of astronomy.
Testing on the joint Nasa and European Space Agency project was finished at the end of August, with shipping preparations under way into September.
Cosmologists, including those in the UK, will use the telescope to map dark matter around galaxies, with the aim of unlocking the secrets of the mysterious substance that makes up the vast majority of matter in the universe.
Caroline Harper, head of space science at the UK Space Agency, said: “The James Webb Space Telescope will be the most powerful and complex telescope ever launched.
“It will advance our understanding of the universe by allowing scientists to hunt for the unobserved formation of the first galaxies and look inside dust clouds where stars and planetary systems are forming today.
“The UK has played a crucial role in leading the international consortium that developed the Mid-Infrared Instrument, which will allow us to examine the physical and chemical properties of objects in the early universe in greater detail than ever before.
“As we move one step closer to launch, we are one step closer to understanding the universe and our place in it.”