The Leaving Cert has been cancelled with students set to get "predictive grades" instead.
Some 61,000 students were due to sit the State exam on July 29.
Education Minister Joe McHugh said: "Unfortunately there is now compelling advice that shows holding the exams and returning to school would be impossible."
Under the revised plans, a system of predictive grades will be given to students in lieu of them sitting physical exams.
Speaking at Government Buildings on Friday, Mr McHugh said Covid-19 has forced the Government to make changes that would have been unthinkable previously.
"The Leaving Cert is important, but it's life that matters," he said.
"The Class of 2020 will never forget the events of this year. I am disappointed that we are unable to run things the same way as in previous years. We are removing uncertainty and providing a clear solution."
Regarding predicted grades, he said it will not just be teachers who give the calculated score as it will be overseen by a school principal.
"Fairness and equity has been kept at the centre of all discussions," he added.
Mr McHugh acknowledged the decision to change the State exam may have legal consequences.
"There are legal vulnerabilities around the course we are taking," he said.
The Education Minister also said a special unit in his department has been designed to oversee and apply a "nationalised standardisation" to Leaving Cert predictive grades.
Mr McHungh said students will have the option to appeal over their grade if they are not happy.
"My preference was for the exams to be proceed. However, proceeding with the exams this summer would have been unfair given the current pandemic."
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