The Britain's Got Talent judge has been smoking for 44 years and currently goes through 15-a-day.
However, the 52-year-old is determined to kick the habit after being reminded of a number of smoking-related deaths in his family and has sought treatment from a clinic in Chelsea.
"Simon made it his New Year resolution," a source told The People. "He's been smoking since a very young age and feels the time is now right to try and stop.
"He has no major health issues at the moment but, as always, he is under a lot of pressure with his work schedule. Simon's mother and some of his closest friends have been nagging him for some time about trying to stop smoking.
"His grandfather was a heavy smoker who died of lung cancer. His father suffered a heart attack. It's made Simon think long and hard about his own health now."
Cowell's Britain's Got Talent co-judge Amanda Holden revealed in 2010 that the media mogul used to smoke in his dressing room during shows.
The pair have been joined by new panelists Alesha Dixon and David Walliams for the upcoming series of the show. The competition launched in Manchester on Friday (January 20).