During 2005 he worked on the stock market listings of technology firms Pure Wafer, Bango, FDM Group and Celoxica. He also led oil and gas accounts with Aminex and Fortune Oil.
Prior to ICIS, Berens worked with Pelham co-founder James Henderson for seven years at College Hill Associates.
Berens' departure leaves ICIS with just one director, chief executive Tom Moriarty, and a further four staff.
Moriarty said he would be hiring a replacement for Berens 'imminently'. He added: 'The financial PR sector is a bit like mercury. People tend to move around.'
Berens' arrival at the now ten-strong Pelham brings technological knowledge to the agency, which previously tended to focus on the oil and gas, mining and financial services sectors.