The British astronaut will be running the London marathon while aboard the International Space Station.
Peake, who arrived on the orbital outpost back in December 2015, will be joining thousands of other runners by strapping himself in to a treadmill and running the entire 26.2-mile course in space.
The only other person to have ever run a marathon in space was astronaut Suni Williams who managed to complete the Boston marathon aboard the station back in 2007.
Preparing to run a race in zero-gravity however presents a rather unique set of challenges.
"I don't think you can ever do enough training for a marathon," said Peake. "The toughest part has been getting used to the harness system. It's like running with a clumsy rucksack on."
"You can get chafing around your hips and shoulders."
With only three days remaining before the event however his time to prepare is now almost over.