O’Shea will lead the Boys in Green on an interim basis for the two friendly international matches against Belgium and Switzerland at the Aviva Stadium next month.
He will be supported by McCarthy – who, as a player, represented his country up until U21 level, and received one senior call-up for a friendly against South Africa in 2009 – as assistant coach throughout the March window.
McCarthy has been associated with Crystal Palace for almost 16 years, having first joined the club in the summer of 2008. The former defender made 151 appearances across eight seasons in south London as a player, before moving into roles as Under-18s coach, Under-23s Head Coach and – last year – joining Palace’s first-team coaching staff.
Marc Canham, Director of Football at the FAI, said: "Paddy has fantastic experience as a coach and is a great addition to the staff. Alongside his current role at Crystal Palace, his experience will prove invaluable to John and the team for these next two matches."
Everyone at Crystal Palace extends their congratulations to Paddy and wishes him the very best in his duties.