Both Ireland and Afghanistan became cricket's 11th and 12th Test nations on Thursday following a unanimous vote by the International Cricket Council during its annual meeting in London on Thursday.
Dublin-born Morgan, a talented left-handed batsman, first played for Ireland as a teenager.
But after securing Ireland's qualification for the 2011 World Cup, in April 2009, he was immediately called up by England after making his mark in county cricket with Middlesex.
Both Ed Joyce and Boyd Rankin, now back in the Ireland fold, made the same switch for similar reasons.
"It is no secret that Ireland chased this dream, number one because Test cricket it is the best, it is the pinnacle format and that which the best players say defines their legacy in the game," said Cricket Ireland chief executive Warren Deutrom in a conference call with reporters following Thursday's announcement by the ICC.
"It was the reason stated by some of our brightest and best in recent years for why they wished to play for England."
Deutrom added: "So therefore, we realised that unless we were sharing the same dream as our best players, we always had the risk of losing them.
"While I can't sit here and say definitively no Irishman is ever going to play again for England, what I can say is at least the reason that the reason given in the past for them to leave no longer exists."
Morgan, now England's limited overs international captain, played the last of his 16 Tests in 2012.
He has repeatedly insisted there is no chance of him reverting back to becoming an Ireland-qualified player.
Neither Deutrom not his equally elated Afghanistan counterpart Shafiq Stanikzai felt able to say when or where their respective countries would play their inaugural Test.
Deutrom said a balance had to be struck been wanting to play that Test as soon as possible and staging it somewhere "appropriate for the occasion". He also said a Test against England at Lord's in 2019 was "feasible".
Stanikzai added he would consult with the "Full (Test) Members in our region".
Afghanistan have recently played their 'home' matches in the Indian city of Noida because of security reasons.
Previous experience suggests it could take both Ireland and Afghanistan a long time to adjust to the demands of five-day Test cricket.
Bangladesh floundered for their first decade while New Zealand took 26 years to win their first Test.
"If they (Ireland and Afghanistan) play each other in their first Test, hopefully it won't be that long," said ICC chief executive David Richardson.
But on a more serious note, the former South Africa wicket-keeper added: "We'll have to take it slowly but surely and be patient."
Richardson also said both Ireland and Afghanistan could expect to see their funding increase.
They currently receive some $20 million over an eight-year period from the ICC and, according to Richardson, the figure could double to $40 million.