He replaces Maurice Pratt, who resigned in early October.
Dunsmore will be joined by two more former members of S&N's senior management team, before it was taken over by Heineken.
Ex-S&N group operations director Stephen Glancey is C&C's new chief operating officer and Kenny Neison - former head of finance for
western Europe at the British brewer - is strategy director.
Pratt resigned after a drop in sales for C&C and the admission that a repositioning strategy adopted for Magners had not paid off.
C&C chairman Tony O'Brien said: "The calibre of these appointments represents a major achievement for C&C and presents the group with an opportunity to address decisively the challenges it faces."