Smith, who has been at the helm of the company which owns both Londis and Budgens for three years, has already been replaced by Donal Horgan, previously MD of SuperValu and Centra in the Republic of Ireland.
Smith joined Musgrave GB in June 2007 from National Lottery operator Camelot Group. He has also held marketing roles with Somerfield and Kraft Foods.
A spokeswoman for Musgrave Group said that Smith was "moving on to pastures new".
Horgan joined Musgrave in 1997 as finance and logistics director. In 2004 he became MD of SuperValu and Centra.
Musgrave GB back in profit as store number hike boosts sales (30 Ocotober 2010)
Musgrave boss Smith named FWD chairman (15 May 2010)