The new, highly contagious variant was confirmed by health authorities in the southern city of Katowice, Deputy Health Minister Waldemar Kraska told lawmakers in parliament, as cited by the state-run news agency PAP.
The Polish health ministry said in a Twitter post that the patient, "a 30-year-old Lesotho national," was being kept isolated and "feeling good" overall.
It elaborated in another tweet that the woman visited Poland's Katowice to attend the United Nations' 2021 Internet Governance Forum, which ended last week.
During the digital summit, she was "staying alone and had direct contact with only two vaccinated people from her country," the Polish health ministry tweeted.
It said the woman "was using personal protective equipment" during the international conference and eating meals in her hotel room after ordering them by phone.
"As an asymptomatic person, she took a test before leaving Poland" and the test came back positive, the Polish health ministry added.
Poland on Thursday reported 22,097 new coronavirus infections and 592 more deaths related to COVID-19, bringing the country's total number of cases during the pandemic to 3,903,445 and fatalities to 90,306.
A range of new coronavirus restrictions took effect across the country on Wednesday as it seeks to fend off the new, highly transmissible omicron variant.
The first Polish citizen diagnosed with omicron was a teenager who tested positive earlier this week during a trip to China, according to a spokesman for the Polish health ministry.