Barwick, 66, has enjoyed a long and distinguished career, spanning over 40 years, with senior roles in both major sports broadcasting organisations and high-profile sports governing bodies.
In December, the former Football Association chief executive was awarded an OBE in the New Year Honours List for services to sport and broadcasting.
The Chairman stated, “After careful consideration I formally told the National League Board in February that I intended to step down at the end of the 2020/21 season.
“I think it is the right time to relinquish the role - and give somebody else the great privilege of leading the organisation.
“Since 2015, I believe the competition has continued to grow in stature and profile, sent strong clubs up into the EFL and built up a formidable and loyal set of commercial and broadcast partnerships.
“Our 66 clubs remain the life-blood of our competition and a vital part of their local communities - and that’s what makes our League so special.
“I also acknowledge just how tough it has been for many of our clubs over the past twelve months facing the unprecedented challenges brought on by the Covid pandemic.
“In closing, I would like to thank my National League Board colleagues, the League’s executive, our commercial partners, the wider football family and, most importantly, our member clubs for their warm welcomes and support over the past six years.
“I will continue to commit myself to the well-being of the National League until the end of the season.
“And, of course, I wish my successor as Chair and everybody connected with the National League my very best wishes for a brilliant future.”
National League vice-chairman Jack Pearce said: “Brian’s appointment signified a change of direction by The National League in 2015 for the benefit of the competition.
“Whilst it would be easy to reflect on what has been a very challenging year for football, not only The National League, the progression of the competition over this six-year period has been greater than we could have expected.
“The Chairman has been influential in our long-term commercial partnerships with Vanarama and BT Sport, with the three-year extensions on enhanced terms this season providing security for member clubs. We have also seen an increased level of professionalism, both on and off the pitch at clubs, since Brian’s appointment.
“Brian’s remarkable work ethic and trust in others have made him an invaluable colleague and a person I consider to be a wonderful friend.”
General manager Mark Ives also added: “Brian has worked tirelessly for the benefit of the League and his vast experience across the game and the media has been a tremendous benefit to the League and its member clubs.
“I have had the privilege now of working with Brian on two separate occasions during my career, and his knowledge and determination has been exceptional. We are all grateful for his support over the years.”