An estimated 200 people are employed at the facility, which has been on the Leeside for over 40 years.
Staff working at the factory were informed about the decision at a meeting on Thursday morning.
There will be no immediate reduction in staffing at the facility, with redundancies not expected until June 2028.
Viatris was formed following the recent merger of generic pharmaceutical company Mylan and Upjohn which was previously the part of Pfizer managing its generics business – mostly Pfizer drugs that had come off patent.
Vitaris said the decision to close came after a thorough assessment of the site, "which unfortunately concluded it was no longer viable due to challenging market and site dynamics.
“In particular, declining demand has resulted in underutilisation of our production capacities at this particular site.”
Viatris will still maintain a significant presence in Ireland, with facilities in Galway and Dublin, even after the closure of the Cork plant.
