The Detroit automaker said the consolidated assembly line will continue to operate until 2016 to meet market demand for the Chevrolet Impala Limited and the Chevrolet Equinox.
The news is positive for the roughly 650 to 700 workers who work on the line, said Ron Svajlenko, the president of local union Unifor Local 222.
"The extension into 2016 gives our workforce some stability and again, we were going through a potential of layoffs and right now that's not the case, so that's very good news for us," said Svajlenko.
"As long as we continue to build vehicles out of that facility, we have the opportunity to remain in the hunt for any kind of long-term additional products that General Motors may need to build."
The Oshawa assembly plant, which employs some 3,500 workers in total, runs two assembly lines. The flexible manufacturing line is currently building the 2014 Chevrolet Impala, Chevrolet Camaro, Buick Regal and Cadillac XTS.
Last month, the Canadian and Ontario governments sold a quarter of their common shares in GM. The governments became shareholders in 2009 when they contributed more than C$10 billion to a bailout to keep the car maker afloat.
In return for their investment, the governments required GM to maintain its share of production in Canada for several years.
(Reporting by Solarina Ho; Editing by Krista Hughes)