Mylan is to create 500 jobs over the next five years through an investment of up to €380m in its Irish operations in Dublin and Galway.
The pharmaceutical company already employs about 700 people here.
Of the 500 new jobs to be added by 2016, about 220 with be based in Galway with the remainder in Dublin.
The expansion is supported by IDA Ireland and also by Údarás na Gaeltachta.
Mylan's operations in Ireland include Gerard Laboratories and Bioniche Pharma.
The planned expansion of the company involves research and development and manufacturing capabilities within its respiratory, injectables and oral solids franchises.
''Ireland has proven to be a valuable location for Mylan, providing the company with access to a skilled and highly educated workforce that shares our strong work ethic and commitment to excellence,'' commented Mylan's chief executive Heather Bresch.
IDA Ireland's chief executive Barry O'Leary said the new Mylan investment and expansion is an extremely positive development for Ireland's life sciences sector.
Mylan is the largest generics pharmaceutical manufacturer in Ireland and is one of the world's biggest generics manufacturer in the world. It employs over 18,000 people globally and is involved in making over 1,000 different products. At the end of last year Mylan had revenues of more than $6.13 billion.
The investment announced to day will amount to €76m per year over the next five years.