"The construction of this bridge will not only connect the two cities, but also promote the integration of the region across borders," said Congo's Planning Minister Modeste Bahati Lukwebo, speaking at the signing in Johannesburg on Thursday.
No start or competition dates have yet been given for the construction of the bridge, but news of it, is already generating excitement.
"It's going to have a great impact," says Papy Mafuto, a member of the Young African Leaders Initiative in Kinshasa.
"It's going to create many jobs. They are going to need more workers from Congo Brazzaville and Congo Kinshasa to implement that project, it's going to create many jobs for both countries," he told RFI.
Currently ferries connect Kinshasa and Brazzaville, the two closest capitals in the world, often at a high price to travellers.
"Sometimes you can pay 10 dollars, at other times the price can go beyond 20 dollars," comments Mafuto.
The new bridge, which will measure about a mile long, and include a four-lane highway, a railroad track and a pedestrian walkway, is expected to bring some of these costs down.
The project is being financed by The African Development Bank at an estimated cost of $550 million.
The project is part of efforts to modernize and improve regional trade. Back in March, 44 countries signed up to a continent-wide free trade agreement, known as the African Continental Free Trade Area (CFTA), to do just this.
Nigeria, and ironically South Africa, where the new bridge project was inked, did not sign up to the CFTA agreement.
Bridge infrastructure gap
What the CFTA and largely this river bridge project illustrate is a willingness to bridge Africa's infrastructure gap.
"Infrastructure: roads, bridges, energy supply, are missing in the region," says Laure Gnassou, an economist, with decade's experience working on the Congos.
"You can have best minerals in the world, without infrastructure, you can do nothing," she told RFI.
Despite its rich supply of natural resources and its large, youthful population, Africa continues to lag behind most of the world in terms of economic development
"Addressing the infrastructure gap will also contribute to unlock the economic potential which is existing in the region," comments Gnassou.
Also worthy of mention, is the fact that both Congo Brazzaville and Congo Kinshasa have been affected by falling commodity prices in recent months, and have no choice but to develop regional trade, in order to diversify their economies.
Some critics however have raised eyebrows at plans to make the bridge a toll bridge, with border posts at both ends, saying this will limit movement to an elite business community, who can afford to pay the charges.
Gnassou disagrees. "The idea is to develop the official trade and try to get rid of the informal trade as much as possible," she reckons.
"You should look at the bridge like you should look at the Inga project. Much more infrastructure done in the region is crucial."
The Inga project Gnassou refers to, is a plan to build a mega dam on the Congo river--quite like this new bridge--capable of producing electricity equal to 20 large nuclear power stations.
The project however has been pushed back several times. And there's also uncertainty about when construction for this new bridge will start, and who will be building it.
Yet, much of it will depend on political stability, a hot-button topic as voters in DR Congo head to the polls next month.
It's a "key ingredient," for Gnassou. Without it "investors, national and foreign investors" will not come.