The deal must be accepted by shareholders of at least 25 percent of Grupo Aeromexico's stock, and is subject to antitrust approvals in Mexico.
“This is the next step in expanding our longstanding partnership with Aeromexico,” said Delta CEO Ed Bastian in a written statement.
Delta and Aeromexico launched a code-share marketing deal in 1994 and have deepened ties in the past few years. Delta bought a $65 million stake in Aeromexico's parent company in 2012.
The two carriers in 2014 opened a jointly-operated maintenance, repair and overhaul center called TechOps Mexico near Queretaro International Airport.
In 2015 they announced a deal to boost Delta's stake, along with options for Delta to buy more shares for a total of 49 percent of the company. Delta and Aeromexico last year agreed to federal terms for antitrust immunity to move forward with a joint venture.