On Barnes' departure his duties will pass temporarily to DMA managing director James Kelly, but the focus of the role could be reorganised as part of the current review of the association's strategy and operations.
Kelly said: "I would like to thank Mike for the immense contribution he has made to the DMA over the years. In particular, his energy, enthusiasm and significant input to the DMA's strategy and business planning have been invaluable. He has spearheaded many initiatives that have helped to ensure that the DMA remains a highly effective trade body.
"However, we're always looking at new ways of developing the DMA to keep it at the forefront of the direct marketing industry. I will therefore be taking the opportunity to review the position in the wider context of the DMA's priorities going forward and determine how it can best serve the interests of our members in these challenging times."
At British Eventing Barnes will take the role of commercial and marketing director.
As reported by he leaves the DMA after ten years, having originally joined as a director in 1999 after a career in publishing and utilities.
Since then his role has expanded to embrace a large remit including membership, communications, awards, events, PR, the DMA's regions and its commercial activities. He also sits on the marketing committee for the Institute of Fundraising.
After several years at British Gas, Barnes joined Emap where he rose to become marketing director for the publisher's consumer magazines.
"What Mike brought to the DMA is energy and a real can-do attitude," said Rosemary Smith, managing director of list firm RSA and a former DMA chairman. "He came from a commercial environment and brought that nous with him, shown in the way he steered the DMA awards which have gone from strength to strength."