The club’s new chairman Darryl Eales has handed the agency the retained account without a pitch.
The brief is to drive up match-day attendance, build relationships within the local community and help improve the match-day experience for spectators.
Eales said: "Seven Dials stood out for us because of its passion, creative approach and experience."
Kelner added: "Football has always been one of my great passions and to work with a club, steeped in history and tradition and which has such ambitious plans, is really exciting. We look forward to seeing them climb up League Two and higher."
Seven Dials has won two other pieces of new business following its sale of a minority stake to Matthew Freud’s company Freuds in July.
Men’s footwear brand Harry’s of London has engaged the agency to build its reputation and influencer network.
And outdoor digital media owner Outdoor Plus has tasked it with a corporate and trade brief.
Kelner said: "We are delighted with the way the business is growing. These are significant accounts, and what’s most important is that they are all brands we believe in. In that way, they fit perfectly within the Seven Dials family."