He replaces Gail Scott-Spicer, who joined the organisation in 2009 and has become chief executive of the Carers Trust.
Hamilton, who joins in mid-May, led the public relations and engagement team at Action for Children for nearly five years.
He will oversee a 26-strong comms team working across media relations, brand development, internal and volunteer comms.
His appointment comes as the association looks to attract more young people from across all sections of the UK population.
Hamilton said: "There's never been a more important time to get more children and adult volunteers involved in a movement that promises huge amounts of fun and adventure, as well as character-building opportunities."
Matt Hyde, CEO of The Scout Association, said: "I am certain he will play a huge part in enabling more young people to experience the life changing adventure that Scouting offers, and showcasing the crucial role that Scouting plays in society to a wide range of new audiences."