Quintus was set up in 2003 by Chris Guyver, a former head of public affairs at Burson-Marsteller. Clients include Betfair, the Rank Group and the Lap Dancing Association.
Sources said talks were at an early stage. They come within months of Quintus losing five staff from its London office (PRWeek, 6 March).
Luther Pendragon partner Simon Whale said: 'Our clear strategy is to invest in businesses in our area of interest.'
He would neither confirm nor deny that talks were under way with Quintus. Guyver could not be reached for comment as PRWeek went to press.