The Beady Eye front man, 40, found his blood pressure dropped into a state of anaphylactic shock after he tucked into a bag of the candied sweets during a hotel stay last month and he has now been diagnosed with a serious nut allergy, requiring him to be equipped with a special injection in case the scenario repeats itself.
Speaking at the launch of The Red House restaurant in south-west London, he said: "I've done some stuff over the years but never, never did I think a f****** blue M&M would be the thing that could have killed me. I was in a hotel on holiday and got in about the mini bar.
"I was bored and hungry, so it's what you do, man. I've always liked M&Ms so I got into them. I had a blue one. My mouth started to swell up and I could feel it tightening my throat, man. I had to go to the docs and get it checked out straight away.
"It happened again a couple of weeks after and now I've got to carry a syringe about with me in case of emergencies."
Liam isn't the only rocker who suffers from the condition.
Mumford & Sons member Ben Lovett has an extreme peanut allergy, which prevents the band flying with British Airways or Virgin airlines due to the possibility of encountering the food.
A source previously said: "Mumford & Sons aren't big on demands. They have the most basic rider and never get funny about what hotel they are staying in.
"But they've become really particular about flying because of Ben's allergy. The last thing they want is for him to go into anaphylactic shock while flying. And they're in the position now where they can be picky."