The Atlanta carrier is the last U.S. airline to lift this restriction, which was put in place last April at the beginning of the coronavirus pandemic.
Delta said it extended the policy due to travelers favoring the airline because of the safety measure.
The carrier said, however, that it's easing the restriction as vaccination rates and demand for travel grow.
Delta Air Chief Executive Ed Bastian said in a statement on Wednesday that 65% of customers who flew with the carrier prior to the pandemic have indicated they "plan to have least one dose of a COVID-19 vaccine by May 1."
This is “giving us the assurance to offer customers the ability to choose any seat on our aircraft, while also introducing new services, products and rewards to support the journey,” he added.
Statistics also show that people are becoming increasingly more comfortable traveling in the U.S.
The Transportation Security Administration says nearly 1.6 million people passed through security checkpoints on Sunday, Dow Jones reported.
In addition to allowing for increased seating, Delta plans to resume snack and beverage service on April 14, media reports say.
"In early June, customers flying in Delta One or first class on select domestic coast-to-coast flights will see hot food options return, and first class customers on other key U.S. routes will enjoy fresh boxed meals beginning in early July," the airline said.
Delta Air shares at last check were trading 1.2% lower at $48.31.