Walker, who officially started in the role this week, will be based in London and will report to chief executive Samir Brikho.
He will be responsible for all the company's external and internal comms, including media, employee, investor, marketing, brand and government relations.
He joined AMEC in May as interim director of comms, replacing Sue Scholes, who became chair of the Investor Relations Society in July following an overlap period.
He was previously global vice-president and head of corporate comms and investor relations at Travelport.
Before that he was a managing director with The Hogarth Partnership and co-founded comms consultancy Gainsborough in 2003.