Akerson said Fairfax will be among the company's most efficient, state-of-the art facilities.
GM employs nearly 3,900 workers at the plant, which has produced more than 12 million vehicles since 1945 and currently builds one vehicle every 58 seconds. The Chevrolet Malibu and Buick LaCrosse are made at the plant.
"It is amazing to have this kind of money put in this plant," said Joan Kelly, a quality engineer manager who has worked at Fairfax for nearly 29 years. "It means we're going to be around for a long time.
"It's a testament to the Midwest work ethic. I'm glad to see this money spent in the middle of America."
An investment this large means that Fairfax could get additional models. At a minimum, it is likely to get future generations of the Malibu and LaCrosse.
"If they're going to be putting a lot of money into a plant like that, you'd better keep it around a while," said Jim Harbour, author of a book on auto manufacturing and the man who developed a widely followed annual measure of factory productivity.
Brownback said the investment would help boost the state's economy. "GM is back, and Fairfax is here to stay," the Republican governor said.
Both the LaCrosse and Malibu have been decent sellers for GM in the past, but sales have slowed of late. U.S. sales of the LaCrosse, a big midsize luxury sedan, fell 2.4 percent last year to just over 57,000, according to Autodata Corp. Malibu sales rose 3 percent to almost 211,000, but that's a little more than half the sales of the Toyota Camry, the midsize leader and the top-selling car in the U.S.
GM launched a new version of the Mailbu in 2012, but it took until late in the year for the full selection of engines to arrive in showrooms. The company has said it will get a quick makeover this year.
AP Auto Writer Tom Krisher in Detroit contributed to this story.