The deal will see Delta continue as the club's Official Global Airline Partner.
Chelsea Managing Director Christian Purslow said: "We are delighted to be entering into a new phase of our partnership with Delta Air Lines.
"Over the next three years we look forward to Delta continuing to help us tell Chelsea’s story all over the world, particularly in their home market in America, where they are such an established and recognised presence."
Perry Cantarutti, Delta’s Senior Vice President, Europe, Middle East and Africa, added: "Chelsea Football Club and Delta are both winning brands and since the partnership began three years ago, both have gone from strength to strength.
"We look forward to another three great years and to working with the club in promoting their activities in the United States."