The work of a team of engineers from Hertfordshire will blast off from the USA's Florida coast on Thursday night.
The Inmarsat 4 satellite, built in Herts, is worth £200m
The world's largest commercial satellite, the £200m Inmarsat 4, was built at satellite manufacturer EADS Astrium, based in Stevenage.
A spokesman said the craft would improve and extend high-speed internet coverage to almost 90% of the world.
The satellite is scheduled to take off from Cape Canaveral in Florida on Thursday night.
'Access remote areas'
EADS spokesman Alistair Scott said the Inmarsat 4 would particularly help businesses which needed internet access from remote areas of the world.
"New businesses can rely on this form of access in remote areas," he said.
"It will be ideal for people in oil companies, who are looking for oil reserves, or for holiday resorts that don't have a normal access point. They can actually use it to directly link up to the satellite," he added.
The satellite is expected to remain in orbit for at least 14 years.
Two identical satellites are also currently being manufactured by EADS Astrium.