File Photo: DR Congo President Felix Tshisekedi and Uganda s President Yoweri Museveni at a past function. AP
The EAC, based in the Tanzanian town of Arusha, now expands to seven nations, counting Burundi, Kenya, Rwanda, Tanzania, South Sudan and Uganda among its members.
EAC chairman Kenyan President Uhuru Kenyatta announced DR Congo's membership, describing it as "momentous".
"Admission of the DRC marks a momentous occasion in the region's integration history," Kenyatta told a virtual summit.
"The EAC now spans from the Indian Ocean to the Atlantic Ocean making the region competitive and easy to access the larger African Continental Free Trade Area," the group's secretary general Peter Mathuki said.
The bloc was founded in 2000 and works to encourage trade by removing customs duties between member states. It established a common market in 2010.
Mineral-rich DR Congo's population of 90 million people will expand the EAC market to almost 300 million.
The country shares borders with all EAC members except Kenya and is already a member of three other regional trading blocs.
The last country to be admitted to the EAC was conflict-wracked South Sudan in March 2016.