Browning spent 24 years with the paper merchant, which he described as "exceptional, simply because of the company and the people I've worked with over that time".
He said: "The corporate responsibility and environmental work I've been involved with over the past three years has created a industry-leading environmental profile for McNaughton and the progress, achievements and eight environmental awards are something that I'm very proud of."
As to the future, Browning said he viewed it as "a great opportunity to find an exciting new challenge".
He is considering several opportunities from the corporate and public sectors within the environmental arena.
McNaughton marketing director Tony Porter said the move is not part of a wide-ranging reorganisation within the group.
He said: "Howard has made a valuable contribution to the company's approach to the environment and corporate responsibility.
"McNaughton remains committed to further development in both areas through the combined resources of our new and enlarged Green Team. We wish Howard every success for the future."
Earlier this month, Browning accepted the award on behalf of McNaughton for one of the Sunday Times' 60 Best Green Companies 2009 - reaching 38th position.
