Reidy's family moved to County Donegal in 1977, and he grew up in Raphoe, Dunfanaghy and Moville.
[1] He attended Carndonagh Community School, and then studied history and politics at University College Dublin.
[3] After graduating, Reidy found work as an organiser for the SIPTU union, for various groups of private sector workers in the West of Ireland.
In 2016, Reidy moved to become deputy general secretary of the Irish Congress of Trade Unions (ICTU), to which SIPTU is affiliated.
On election, he listed his priorities as strengthening collective bargaining, increasing membership of the trade union movement, and giving workers a greater voice in society and the economy.