Niel has secured the $445 million deal through his private investment vehicle, and Niel also controls French low-cost operators Iliad and Free,
The move is a further sign of CWC’s desire to move away from regions outside of its core focus in Central America and the Caribbean.
Last year, CWC struck a deal with Bahrain's Batelco to sell its stake in Monaco Telecom but it fell through.
Once the deal has been finalised, the firm has said that it will generate all of its revenue from the Caribbean and Latin America region.
"We have enhanced the services available to the residents and businesses of Monaco and achieved good returns," said Phil Bentley, CEO of C&W. "However, as we concentrate our business on the Caribbean and Latin America, we have taken this opportunity to crystallise the value we have created."