The affiliation is designed to expand Edelman's African operation outside of its office in Johannesburg, South Africa, the agency said.
Alongside the Johannesburg office, the world's biggest PR firm already has partners in Kenya and Egypt.
"Our decision to partner exclusively with Chain Reactions Nigeria was informed by the team's unique understanding of the Nigerian market," said Robert Holdheim, CEO of Edelman South Asia, Middle East and Africa.
According to its website, Chain Reactions Nigeria's roster of clients includes Durex, Nurofen and home fragrance brand Air Wick.
Yesterday, Edelman also announced the appointment of Rupen Desai as its executive vice chairman for Asia-Pacific, the Middle East, and Africa. Desai will be responsible for securing strategic and creative-led brand work for the agency across the region.
The world's largest marcomms group, WPP, has also been expanding its African footprint recently.