Maynard, who joins the association next week, will take charge of internal communications, strategy and policy at the body.
Marketing director Martin Cottingham said the board had decided to remove some of the day-to-day management duties from the role so Maynard could concentrate on high-level strategic work.
'The role covers everything from hard-hitting policy campaigns around the impact of farming on climate change to consumer campaigns promoting the health and taste benefits of organic food,' said Cottingham.
Maynard will also be charged with raising awareness of the group's charity status and the work it does beyond the certification of organic products.
'The organic movement is bigger than ever so this is an exciting time for the Soil Association,' Maynard told PRWeek.
'Its Food for Life campaign inspired Jamie Oliver's work on improving school meals, and people are realising organic food isn't just something that concerns the well-off.'
Maynard was previously the Soil Association's acting head of campaigns before leaving to set up sustainable farming lobby group FARM in 2001.