Hewer will act as a trouble shooter for small family farms and will aim to boost their businesses in tough economic times.
The Countdown presenter said: "The small family farm is the backbone of the UK countryside. I wanted to use everything I had learnt, over the past 40 years of business, to help them come through this difficult time."
Hewer will offer his expertise to five farms, developing projects such as harvesting seaweed to brewing beer, producing flavoured pet water and entertaining cruise ship groups.
Lord Sugar's close aide's motto throughout the show is "doing nothing is not an option" and he faces stiff resistance from a number of the farms he works alongside.
The Farm Fixer starts on July 9 on BBC Two.