The case is associated with travel from one of the southern African countries that have been declared by the Irish government as high-risk countries for the spread of the new variant, said the department in a statement, without giving further details.
The Irish national radio and television broadcaster RTE reported earlier in the day that the Dublin-based National Virus Reference Laboratory had carried out tests on a number of samples over the weekend and one of the eight samples that underwent genome sequencing was confirmed having the Omicron variant.
The report said scientists are not aware of any additional cases associated with the confirmed case, and there is no evidence of community transmission of the variant so far.
The Irish government last Friday declared seven southern African countries as high-risk countries where the Omicron variant was first detected, advising against all non-essential travel to and from these countries by tightening the issuance of visas.
The seven countries are Botswana, Eswatini, Lesotho, Mozambique, Namibia, South Africa and Zimbabwe.
The government also ruled that Irish citizens returning home from these countries shall undergo strict home quarantine with two PCR tests during quarantine.
The Irish Department of Health on Wednesday reported 3,793 new COVID-19 cases, bringing the national tally to 573,905.
To date, there have been a total of 5,707 deaths related to COVID-19 in Ireland, including 55 deaths newly reported in the past seven days, said the department.