It is widely speculated that the bid came from US private equity group Madison Dearborn Partners, although no formal offer has been made.
Tulchan founder Andrew Grant leads the brief, which was won following a non-competitive pitch.
The agency reports to the Smurfit board, headed by chairman Michael Smurfit and CEO Gary McGann.
The brief is to advise the company's board on media strategies surrounding the offer, communicating with the business press and investors.
Tulchan will work with Smurfit's retained US agency Taylor Rafferty for communications work in the US.
The agency confirmed it has also been hired to handle PR for Intertek Testing Services' (ITS) stock market flotation, which is set to value the firm at between £900m and £1bn.