He worked at Nasa's Jet Propulsion Laboratory in Pasadena for five years, before leaving to set up the finance company Wilshire Associates, through which he made his fortune.
Tito is on board a Russian supply ship as a passenger, riding with two veteran cosmonauts. The flight makes the 60-year-old the 415th person in space - and the first as a paying traveller.
The flight is a dream come true for the Californian financier, who has been trying to join the elite club of space travellers for decades.
Hard fight
"It is not going to be a holiday (but) to me it is a life's dream and the start of a new career," Tito told journalists, during a break from training for the mission.
Tito, from Los Angeles, started his career as a space scientist, designing flight trajectories for three historic Mars missions in the 1960s.
He worked at Nasa's Jet Propulsion Laboratory in Pasadena for five years, before leaving to set up the finance company Wilshire Associates, through which he made his fortune.
But despite his millions, Tito has had to fight to blaze a trail for a new generation of adventure tourists.
He first looked into a space vacation in 1991, on a trip to Moscow. And when he did finally get hold of a ticket into space he suddenly found it to be null and void thanks to Russia's decision to scuttle the Mir space station before it fell uncontrollably from the sky.
Civilian history
Russian space officials later offered him a ride on a Russian rocket ship supplying the ISS. Tito's former employer - Nasa - initially objected to the trip, citing safety concerns.
But international space officials finally agreed that Tito could fly, subject to him signing a deal relieving all national space agencies of responsibility in the event of a tragedy.
Tito also signed a contract saying he will pay for any breakages he causes and he is banned from US segments of the ISS unescorted.
Tito may be the first to pay for a trip into in space, but he is not the first civilian to make the journey. One of Nasa's early attempts to put a non-professional in space ended in disaster when teacher Christa McAuliffe and the crew she was flying with were killed in the Challenger explosion in 1986.
Tito also follows confectionery scientist Helen Sharman, who in 1991 beat thousands to become Britain's first astronaut, a Japanese journalist and a member of the Saudi royal family, who both went to Mir.