Hamer, who started this month, will work on a number of the agency's key accounts, helping clients with their media, public affairs strategies and stakeholder engagement.
Prior to joining Portland, Hamer was editor of business and economic news on BBC's Radio 4 Today programme and editor of digital coverage of business and technology news for the corporation.
He will report to Portland's new head of corporate Sam Ingleby, who said: "Simon will bring a fantastic skillset to our fast growing corporate team. His outstanding career in journalism and his expertise in media, and digital platforms, will enable us to develop our capabilities allowing clients' stories to reach and engage a variety of audiences."
Portland's corporate division is made up of 80 consultants, and includes work across public affairs, digital, research and insights, local and financial communications.
Hamer is the latest in a series of hires at Portland. Last month the agency announced the appointment of three former Downing Street advisers and earlier this month, former Weber Shandwick vice president Lucy Jenkins joined the agency's philanthropy practice as a partner.
A spokesman for Portland said: "We are having another year of strong growth, and as ever we are investing to make sure our core capabilities remain the best in the business, and to expand into new areas like our Singapore office."