The news emerged this morning in a statement issued in response to a story in the FT that S4 is looking to buy US programmatic firm MightyHive.
Regarding its appointment, Powerscourt said: "The TMT team led by Elly Williamson, with CEO Rory Godson and managing partner Victoria Palmer-Moore, will support the acquisitive new era media company. John Elliott and Celine MacDougall complete the team. The team's other clients include Micro Focus, Cineworld, and CrowdCube."
PRWeek understands the appointment was made without a competitive pitch.
Former WPP CEO Sorrell’s personal communications is being handled by David Rigg, founder and managing director of Project Associates.
The statement released this morning about the rumoured MightyHive acquisition says: "There can be no certainty as to whether any transaction will occur nor as to the terms of any possible transaction. Further announcements will be made as appropriate."
Speaking to PRWeek last week, Sorrell said he believes the boundaries between what PR and ad agencies do in digital media is increasingly blurred, and S4 Capital would consider acquiring a "small to medium-sized" PR agency if it has the right social content capabilities.
Financial and corporate PR specialist Powerscourt was founded in 2004 by Godson, former Sunday Times business editor and ex- Goldman Sachs corporate affairs chief.