The managing director of St Boswells-based auctioneers John Swan Ltd will call it a day next April after 48 years of selling livestock.
Mr Clark told The Scottish Farmer: "I'm not departing the scene completely. I'll become a non executive director of John Swan and Sons PLC and I'll still have an interest on what's going on in the market."
Meanwhile Mr Clark's brother Michael, chairman of Lawrie and Symington confirmed this week that Graham Burke has resigned as manager of the firm's Forfar market.
Mr Burke, along with cashier Neil McAllan were suspended two weeks ago following allegations of irregularities.
Said Mr Clark: "As our investigation is still on going I can make no further comment at this stage."