Randall, who herself events, joins from PDSA where she worked on consumer campaigns to position the organisation as the UK's leading veterinary charity.
Prior to that Randall ran her own PR company working on agri-business accounts, as well as crisis and recovery campaigns with the National Farmers' Union.
She will take up her position at British Eventing on Tuesday March 25.
Mike Etherington-Smith, British Eventing's sport director, said: "We feel Liza will prove to be a valuable member of the team.
"Both Liza and Annalise (British Eventing's marketing and sponsorship manager) have some very exciting plans for British Eventing, leading up to 2012 and beyond and we look forward to helping them bring their ideas to fruition."
British Eventing is the national governing body for eventing in Great Britain and regulates the sport as well as organising and scheduling many events throughout the country.