The aeroplane is a larger version of its new CSeries aircraft.
The Montreal-based plane and train maker is under pressure to bring the CSeries into service after years of cost overruns.
The smaller CS100 started testing in 2013. The wings and engine covers of the CS300 jet are made in Belfast. The aerospace company is one of Northern Ireland's biggest employers.
About 5,000 permanent employees and about 1,000 temporary and contract staff work at its Belfast base.
Michael Ryan of Bombardier Belfast said: "It is another testament to the skills of our workforce, and our design and manufacturing capabilities, which are helping bring a step change in aircraft wing technology."
Bombardier Inc has launched a test flight of its CS300 jet.