RMG is the umbrella organisation for 34 racecourses, which hold an interest in Racing TV, Racing TV International and Racecourse Date Company.
Mullen was most recently CEO of Ladbrokes Coral. He had previously held the position of Managing Director of Ladbrokes Digital and Chief Operating Officer of William Hill.
Britt is Chief Experience Officer at Kindred, having previously held the position of Chief Operating Officer and Business Development Manager at the operator.
Both have been brought in to these independent roles to help the RMG Board understand the challenges that face the gaming industry, as well as provide strategic advice.
Antonia Wright has also joined as Company Secretary and Legal Director. Wright is currently Head of Commercial Legal Affairs at The Stars Group.
Roger Lewis, Chairman of RMG, said: "These new appointments will enhance the RMG Board’s desire to work closer with the betting and gaming industry.
"Jim and Britt will provide RMG with a better understanding of this critically important driver of our business and will help us build stronger relationships across the industry."
