The hire takes Newgate’s UK public affairs team, which reports to managing partner Simon Nayyar, to six people.
Black was head of media and director of trade and government relations in the public affairs practice at law firm DLA Piper.
His clients have included high-net-worth individuals, multinationals and investment firms and his experience of litigation-linked communications is being seen as a useful asset by Newgate.
Nayyar said: "We’re thrilled Eben has chosen us over a number of other agencies he was talking to."
Before Black joined DLA Piper he was chief political correspondent of The Sunday Times and before that was political editor of The News of the World.
Black is one of two partners in Newgate’s UK public affairs team; the other is former Liberal Democrat aide Gareth Jones.
He cited Newgate’s "ambition and vibrancy" as his motivation for joining the agency.
Newgate has six people in its public affairs team in Brussels as well as a presence in Hong Kong, Singapore and Australia.
The government relations practice at DLA Piper was set up by Lord Tim Clement-Jones, who chaired it between 1999 and 2010 but is no longer involved with it.