Mr Marshall, a former Agriculture and Western NSW Minister, will be stepping down from his role next month to pursuing opportunities in the corporate world and in his own personal life.

"This is not a decision I have made lightly, but it's one I'm now very comfortable with," Mr Marshall said.

"Put simply, I feel it's time for me to move on and take up new challenges."

Mr Marshall, 39, first got into politics at the age of 19 when he became a Gunnedah Shire councillor following in the footsteps of his father, a former Gunnedah Mayor Geoff Marshall.

He then became Gunnedah's youngest mayor at the age of 22 from 2007 to 2012 before being elected as the Northern Tablelands MP 11 years ago.

"Coming into this role 11 years ago, it was never my intention to stay forever, believing that our region is best served by those prepared to get in, give it everything they have and then pass the baton on to fresh hands. Hopefully I have done this," Mr Marshall said.

"I have thoroughly enjoyed my years in public life serving the communities of Gunnedah Shire and now the people of the Northern Tablelands, as a councillor, Mayor, State MP and a Minister.

"Their support for me has been overwhelming and heart-warming. It's been an honour and a privilege to serve rural communities and country people and I thank them sincerely for that opportunity over the last two decades.

"We have achieved some incredible things together and I will always cherish the friendships I have made and the interaction I have had with people during my time in the role."

Mr Marshall said it was a demanding and "all-consuming" role to do properly and it inevitably took its toll.

"I've come to the conclusion that despite absolutely loving our region, its people and my role as a local State MP, I cannot put this move off any longer. This will be the end of representative politics for me," he said.

"While there will be plenty of time for reflection over the next five weeks and beyond, for me, I'm firmly focused on the work I still have to do, which I intend to carry out with the same enthusiasm and energy as I always have."

Mr Marshall, who made the announcement during a meeting of Mayors across his region in Inverell, will formally hand his resignation as the Member for Northern Tablelands the Speaker of the NSW Legislative Assembly on May 13.

NSW Farmers' vice president Rebecca Reardon said Mr Marshall would be remembered by farmers for fighting for drought support, grants for community development, prevention of rural crime and improved biosecurity.

"Adam was passionate about serving his electorate and wider regional Australia. He was a regular at community events across the northern tablelands and listening to his constituents," Mrs Reardon said.

Leader of the NSW Nationals Dugald Saunders said since winning the Northern Tablelands seat in 2013, Mr Marshall had been a great local member and advocate for his community.

"Whether bushfires, drought, COVID-19 or the escalating regional crime crisis, Adam and the NSW Nationals have always had the region's best interests at heart," Mr Saunders said.

"On behalf of the NSW Nationals, I would like to thank Adam for his service and wish him all the best in the future."

He said the NSW Nationals had a bold vision for the Northern Tablelands, which his government invested record amounts in health, education, transport, and roads.