He took off onboard a Soyuz TMA spacecraft from the Baikonur Cosmodrome in Kazakhstan on Saturday with the expedition 15 crew and docked at the ISS last night at 20:10 BST.
Dr Simonyi said that he feels "very lucky" to be the world's fifth civilian space tourist.
"I consider my mission to be a small part of an important trend to make space accessible to more people," he said.
"I hope to share my mission with many others through my website, www.charlesinspace.com, which I will continue to update during my time on the ISS."
Dr Simonyi will return to Earth on April 20th along with expedition 14 crew members Commander Michael Lopez-Alegria and Flight Engineer Mikhail Tyurin.
While in space he will complete more than 190 orbits of Earth and travel about five million miles. Dr Simonyi will also tuck into a feast prepared for him by his close friend, the lifestyle guru Martha Stewart, including roasted quail and duck breast.
In preparation for his spaceflight, organised by the company Space Adventures, Dr Simonyi undertook a training programme at the Yuri Gagarin Cosmonaut Training Centre located in Star City, Russia.
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