Glanbia's managing director John Moloney has formally resigned from his post today, but will remain with the company until the end of the year.
As previously announced, Siobhan Talbot takes up the managing director role with immediate effect.
Ms Talbot was previously the company's group finance director. She has been a board member since 2009.
The food group today also announced that Mark Garvey will replace Ms Talbot in the finance role. Mr Garvey is joining Glanbia from the Sara Lee corporation.