"Risk is part of our profession", the 54-year-old said.
A Russian-made Soyuz rocket blasted a three-man crew into orbit on Monday, beginning the first manned voyage to the International Space Station since a mission in October was aborted in midair because of a rocket malfunction.
Their Soyuz MS-11 spacecraft entered a designated orbit just under nine minutes after the launch and is set to dock at the space outpost in about six hours.
A Soyuz-FG rocket carrying NASA astronaut Nick Hague and Roscosmos' Alexei Ovchinin failed two minutes into its flight on October 11, activating an automatic rescue system that sent their capsule into a steep ride back to Earth.
The evening before the launch, crew commander Oleg Kononenko said the astronauts "absolutely" had trust in the flight preparations.
Saint-Jacques, 48, described the Soyuz spacecraft as "incredibly safe".
Afterward, investigators said they believed other Soyuz models may have been defective, but said additional checks had been introduced.
Saint-Jacques will be the first Canadian astronaut to visit the space station since Chris Hadfield, who recorded a version of David Bowie's "Space Oddity" on board in 2013.
In a successful rehearsal for Monday's flight, a Soyuz cargo vessel took off on November 16 from Baikonur and delivered several tonnes of food, fuel and supplies to the ISS.
The mission marked the 100th orbital launch of 2018, and the first time in 28 years that humanity reached that number of launches within a calendar year.
There, they'll meet the European Space Agency's Alexander Gerst, NASA's Serena Auñón-Chancellor and Roscosmos' Sergey Prokopyev, the current crew of the ISS who'll use the Soyuz to return to Earth on December 20.
During their mission, members of the crew are scheduled to embark on a spacewalk to further probe a mysterious hole that caused a loss of air pressure on-board the ISS in August.
The experiment could pave the way to new treatments for muscular conditions for people on Earth, according to the UK Space Agency.