Alastair Hetherington, 57, said he was embarrassed and devastated by the case, which was brought against him after he walked out of the store without realising he was still holding the items.
A jury at Belfast Crown Court spent one hour on Wednesday considering their verdict before unanimously acquitting the accused.
Mr Hetherington, of Lisolvan Terrace in Brookeborough, Fermanagh, was arrested in February last year when he was stopped by a security guard as he stepped outside the store to get a clear signal on his mobile phone.
Desmond Fahey, for the defence, said his client had forgotten he was still clutching his shopping, which also included a vase of flowers, skimmed milk and juice.
Security staff at Marks and Spencer became suspicious when Mr Hetherington left the food hall without paying for his shopping.
They watched on CCTV as he picked out a shirt and tie in the gents department and then sat on a chair next to a side exit door.
Mr Hetherington then went to leave and walked down steps but appeared to stop and turn as if to go back when he was approached by a security guard.
The jury rejected prosecution claims that Mr Hetherington, a tour manager, had purposely left without paying and, when stopped, told a security guard: "OK, you got me".
He told the court he had made a "genuine mistake through stupidity and tiredness" as he tried to text a friend.
Mr Hetherington explained that in the 24 hours before he was arrested, he had travelled with a tour group to Scotland and Manchester to see United play, and then back to Belfast via Dublin.
"As far as I was concerned I was stupid and forgetful and had done nothing wrong," he said, adding that the experience had left him "totally embarrassed and devastated".