The $1.6-billion deal to buy 54.2 percent of Telenet, a division of French telecommunications giant Alcatel, would bring Callahans total number of European cable subscribers to 6.6 million.
"This is a very healthy addition to our overall holdings," said Andrew Sukawaty, Callahans London-based president and chief operating officer.
Callahans subscribers on the continent will grow to 8.8 million when a separate deal in Baden-Wurttemberg, Germany, closes soon, Sukawaty said.
Callahan, headed by former US West International chief Dick Callahan, invested in its first European cable systems in Spain and France in 1999.
A year ago, it joined the ranks of the largest European cable companies when it won a bid for controlling stake in Deutsche Telekoms 4.4 million-subscriber North Rhine-Westphalia franchise.
Sukawaty said Callahan Associates has been working on the Telenet acquisition since May of last year.