Reporting directly to the partnership's chairman Charlie Mayfield, Moys will head a 20-strong team.
At Cadbury, Moys was global internal and interactive comms director during its controversial takeover by US food conglomerate Kraft Foods.
He takes overall responsibility for the partnership's media relations, public affairs and internal comms, including its weekly magazine, The Gazette, and the John Lewis Partnership website.
Previous comms head Susan Donovan left the group at the end of January to take a career break abroad. Helen Dickinson remains as head of press and PR for the John Lewis retail business, while Christine Watts continues as comms director for Waitrose.