In his new role Johnson will manage the marketing of Global’ brands, which also include LBC and Gold, and will report into Stephen Miron, the group chief executive at Global.
Johnson is the marketing director for mobile devices at Microsoft, a role he started in July 2014 following Microsoft's purchase of Nokia.
He was at Nokia from 2006 in several marketing roles, including head of consumer marketing and marketing director, and managed the launch of the Lumia brand.
Miron said: "Adam has impressive experience right across the marketing spectrum with outstanding digital credentials and exactly the skills and drive needed for the Global family of brands and we look forward to Adam bringing this talent and experience to Global."
Johnson will take on the role in May. He said: "I’m a big fan of what Global has created and their ambition for the future. As content, media and technology continue to converge around us, I hope my experience and passion for all these areas will help continue to accelerate Global’s growth."
Pearman has been the director of marketing at Global since 2009. He will work out his notice and is "exploring other opportunities", according to Global.