"Based on the thorough review of the CSeries program after the first flight of the CS100 on September 16, 2013, the flight test phase will require more time than originally anticipated to ensure, amongst other things, that the aircraft has the overall system maturity to support a successful entry-into-service," the Montreal-based company said in a statement.
The medium-range aircraft is Bombardier's entry into airspace dominated by Airbus and Boeing.
It will likely compete with the Boeing 737, Airbus A318 and A319, as well as Embraer 195.
The first CSeries jetliner was originally scheduled to be delivered to customers in September 2014.
The launch of the 100-125 seat CS100 now has been pushed to the second half of 2015, followed by deliveries of the slightly roomier CS300 some six months later.
Delays were widely expected, and market reaction was muted. The company's stock price rose slightly in early morning trading.
At the same time, the company announced an order for 26 aircraft from Saudi Gulf Airlines, the newly launched national carrier of Saudi Arabia, worth up to US$1.99 billion.
This brings to 198 the number of firm orders for the CSeries from 17 customers and lessees, who have also secured options for another 247 planes.