The Communications Minister Alex White says he has accepted the resignation of Christoph Mueller as An Post chairman.
Mr Mueller asked to be released from his duties as chairman, as he is taking up a new position earlier than planned.
He is to become chief executive of Malaysia Airlines, in effect from May 1st.
The Public Appointments Service (PAS) will advertise for a replacement at An Post shortly.
Mr White said: "I have accepted Mr Mueller's resignation with regret and I want to thank him warmly for the excellent service he has given to An Post over the last two years."
Mr Mueller was appointed chairman of An Post by former Communications Minister Pat Rabbitte back in 2013.
He has also held leadership roles in Deutsche Post and DHL, before joining Aer Lingus as its chief executive in September 2009 - a post he stepped down from earlier this year.
He was also appointed to the board of Tourism Ireland in January 2012.