Three hundred jobs have been created in expansions by pharmaceutical giant Allergan and leading IT consultancy firm Accenture.
Taoiseach Enda Kenny described the jobs boost as a significant vote of confidence as he attended Allergan's Westport facility for the announcement.
"Developments like this will help us on the path to economic recovery," he said.
US multinational Allergan is to take on 200 staff in a 350 million euro investment at the plant to meet growing demand for its Botox product in treatment of migraines and incontinence.
Mr Kenny added: "Allergan's Westport facility is an important strategic site in their network and contributes more than 50% of global revenues from a range of products manufactured here. The expansion of this facility is a much needed boost for the region and will bring further high quality jobs to the west of Ireland."
Pat O'Donnell, Allergan Pharmaceuticals Ireland managing director, said: "Based on Allergan's present strategic plans, we anticipate that demand for Botox will continue to grow."
Allergan, which employs 900 people in Ireland, will take on 200 new staff at the Westport site over the next four years. It is estimated another 250 jobs will be created indirectly locally during the construction period.
Accenture is to hire 100 graduates and experienced specialists as it expands operations helping clients cut costs, increase efficiencies and support growth nationwide.
Accenture already employs more than 1,000 people in Ireland and provides management consultancy, technology services and outsourcing to the private and public sector including Microsoft, Kerry Group and the Revenue Commissioners. New roles will be available for experts in Java, SAP, cloud computing, mobility and workplace collaboration technologies.
The latest jobs boost at the company is on top of the investment at the Accenture Analytics Innovation Centre, which opened in Dublin last year.