Duncan was previously co-group MD with Baiden, who PRWeek revealed had left after 18 years with the agency.
The co-group MD roles, which included oversight of the various divisions within Red, have been dispensed with.
Mike Morgan, CEO, explained that Duncan's position would lead to a 'simplifying' of the agency structure.
Previously, Duncan oversaw the consumer life and health groups and Baiden oversaw the consumer play, tech and corporate groups.
‘We've got more market-facing management and less general management,’ Morgan said, 'with the deputy CEO role floating across the different groups and their MDs.'
Of Duncan, he added: 'Over almost two decades, Amanda has been a key player in the Red success story. In this new senior role her experience, creativity and drive will be vital ingredients in the agency’s future development.'