The deal also includes options for another 50 C-series aircraft and the option to substitute larger CS300 aircraft.
Delta will be the U.S launch customer for the CS100. The order is a score from Montreal-based Bombardier, edging out heavyweights Boeing and Airbus for the deal. It's also the largest order in Bombardier's history.
Based on the list price for the CS100, the order for the 75 aircraft could be valued at $5.6 billion, though airlines typically get deep discounts for large orders.
Delta incoming CEO Ed Bastian said attractive pricing helped influence the airline's decision to make the order.
During a press conference at a Bombardier facility in Mirabel, Quebec, Bastian said he believes the order makes Bombardier "a third competitor," along with Boeing and Airbus. "And we're thrilled to be able to have that choice in the marketplace."
Delta will be the world's largest operator of Bombardier planes. And with the order, Delta will no longer add up to 20 Embraer E190 jets to its fleet as it has previously planned.
Bastian called the aircraft, which use composite materials and other advanced technology, a "solid investment" with an expected 20 percent improvement in fuel efficiency and more flexibility. The planes also produce less noise and emissions, according to the airline.