Joel Kowsky/NASA via Getty Images
At 11.03AM GMT, his Soyuz rocket will launch from Kazakhstan - finally docking with the ISS several hours later, at 17.23PM GMT.
Peake won't be the first Briton ever to go into space. But he is the first Brit to be selected by the European Space Agency to become an astronaut.
In fact, Peake is - technically - British astronaut number four. There is also Helen Sharman, who became the first Briton in space in 1991 thanks to a deal between Russia and British businesses. Then there's Michael Foale, who has dual British-American citizenship, who first flew with NASA in 1992 and became the first Briton to spacewalk in 1999. And lastly there is the British-South African Mark Shuttleworth. He went into space in 2002, as a citizen - the second "space tourist" paying their way into orbit.
Peake is being accompanied on his journey by two others - American Tim Kopra, and Russian cosmonaut Yuri Malenchenko.
.@astro_timpeake @astro_tim & Yuri wave goodbye before taking lift to #Soyuz spacecraft. #Principia #GoodLuckTim pic.twitter.com/rwOVJTAZ7j
- ESA Operations (@esaoperations) December 15, 2015
You can watch the European Space Agency's coverage live here, starting at 10AM GMT:
The British astronaut is a former pilot who attended military college Sandhurst, leaving the army in 2009. He is 43 and has two sons. Peake is also a keen athlete, and as The Telegraph has reported, plans to run the London marathon while in space.
BREAKING NEWS: @astro_timpeake will run the Digital #LondonMarathon from space raising awareness for Prince's Trust. pic.twitter.com/4AhoyxhRtl
- The Prince's Trust (@PrincesTrust) December 4, 2015
I love this photo from this morning's rollout - en route to Gagarin's launchpad. Don't miss Horizon @BBCTwo 8pm pic.twitter.com/xkSLEsr49e
- Tim Peake (@astro_timpeake) December 13, 2015
This is the door I'll sign tomorrow before leaving to suit up - recognise any signatures @Astro_Alex? #Principia pic.twitter.com/LJ0tfBt2Jk
- Tim Peake (@astro_timpeake) December 14, 2015
Last tweet before launch - GO for flight! Thanks for all the good luck messages - phenomenal support! #Principia pic.twitter.com/8jbxejHEEe
- Tim Peake (@astro_timpeake) December 15, 2015
Tributes to Peake are appearing across the internet ahead of his historic flight. Just take a look at the homepage of Google: