Pearmain will leave the agency this week and start at O2 on 20 September. He will be responsible for social media strategy across the UK.
He said: ‘For a business all about connecting people, social media represent an important and exciting opportunity to build fans, strengthen customer relationships and ensure the brand is at the forefront of innovation in comms.’
Nicola Green, head of PR, O2 added: 'From our perspective, this is a very important hire, not only from the comms perspective but also for the business as a whole.
'We aim to be the best in class in social media and Alex will be very competent in helping us to drive that.'
Pearmain’s hire follows O2’s appointment of former Downing Street aide Theo Bertram as interim head of public affairs.