Their departure will coincide with the end of their earn-out period following the 2005 deal that saw the Canadian marketing group Cossette take a 51 per cent stake in MCBD.
Briginshaw plans to pursue his interests in photography, while Duffy will concentrate on writing. Neither intends to return to the agency scene.
Danny Brooke-Taylor, who joined MCBD as the creative director from TBWA\London two years ago, will assume full control of the creative department.
Briginshaw said: "We have good succession management in place and we feel it's the right time to let ourselves go."
The pair have worked together for almost 30 years. They left Abbott Mead Vickers BBDO in 1999 when they founded MCBD along with two other AMV senior executives, Jeremy Miles and Helen Calcraft.