Miguel Southwell, general manager of Hartsfield-Jackson International Airport, was terminated with a letter sent by courier last Friday.
Atlanta Mayor Kasim Reed said he was in meetings in New York when the termination happened.
The letter is signed by Atlanta chief operating officer Dan Gordon, and says it is "to memorialize our telephone conversation earlier today, which was necessary because you were unable to meet at 10:30 this morning."
The letter continues: "As discussed, your services are no longer required by the City of Atlanta. You were given the opportunity to submit a resignation in lieu of termination, but declined to resign at this juncture."
Southwell has not responded to requests for comment.
Reed appointed the airport's chief financial officer Roosevelt Council as the interim general manager of Hartsfield-Jackson.
At an airport event Tuesday morning, Council said: "We're going to get back to a lot of the basic core things. What's important for us is that we manage our lines. We make sure that the customer, who is really our clear focus, is addressed in every possible way."
"We have incredible people who can get this job done," Council said.