Telling had been with Bell Pottinger for more than 17 years, during which time he managed the reputation of several of its EMEA government clients, and advised companies in the financial sector.
There are no plans to replace him, an agency spokesperson told PRWeek.
He began working at Newgate Communications earlier this month, and reports to the agency's chief executive Gavin Devine.
"Telling has an unmatched reputation for delivering strategic campaigns for clients here and across the world," Devine said.
Telling is also an advisory board director at E2Exchange, a networking group designed to help entrepreneurs grow their businesses and find investment.
Newgate Communications was established in 2011 by Porta, which also owns Publicasity and PPS Group, and has a controlling stake in PR firm Thirteen.