Mr Casey, from Derry, had been considering contesting the election either in Donegal or a Dublin constituency since he announced his intention to run in January.
The two three-seat Donegal constituencies, North East and South West, will come together as one five-seater for the next election.
Mr Casey set up a business in 1995 in Atlanta, Georgia. He recently bought a home in Donegal.
Speaking to Highland Radio News he says Donegal has been let down by politicians for decades: