Keogh has been in the UK role since August 2013. He joined William Grant in 2009 as a senior marketing manager from Barclays.
MacRae, meanwhile, has worked for the distiller in a series of senior marketing roles since 2008. He spent 18 months as vice-president – brand marketing for the US, before moving to his current role, heading up the Tullamore Dew and Hudson Baby bourbon brands, in February 2014.
Both men will start in their new roles on 1 January as part of an organisational shake-up at the company, whose brands include Grant’s, Glenfiddich, Sailor Jerry and Hendrick’s. The change sees the business organised into three regions: EMEA, Americas and Asia.
Neil Barker, managing director UK & Ireland, said: "Gary has been monumental for the UK business and I admire the passion he has for William Grant & Sons’ "dram by dram" approach to building brands for the long-term. He will be a fantastic asset to the new EMEA region.
"Caspar brings with him a wealth of international knowledge and experience of working with our brands and business. I know he will settle in quickly as we begin our 2018 journey and I look forward to working with him as we enter a new phase of growth."
Keogh added: "Caspar shares my passion for brand building and engaging employees to unleash their own independent spirits, and I have no doubt that he will lead the UK marketing team from strength to strength."