But Mr Carr, 73, who stopped smoking at 50, believes that passive smoking may have contributed to his illness.
The former chartered accountant spent 23 years in smoke-filled rooms treating smokers at his clinics. Until recently, his approach was to allow smokers continue to smoke at the clinics.
Mr Carr, who was at home with his family in Surrey this weekend, said he saw his illness as an opportunity to redouble his efforts to cure the world of smoking.
While he was shocked after a regular health check picked up the cancer last week, he remains upbeat.
“I have been the happiest man in the world since I stopped smoking 23 years ago and I still feel the same way,” he said.
Mr Carr’s first Irish clinic was held in Dublin in June 1998. Five Carr-trained therapists now operate in Dublin and Cork.
John Dicey, Carr’s business partner and publicist, said Carr believes that if he contracted lung cancer as a result of years in smoked-filled rooms delivering his message, it was a price worth paying for curing around 10 million smokers.
Mr Dicey said his partner had no plans to give up work just yet. “He is enthusiastic about the time he has left and is doubling his work, which is fabulous,” said Mr Dicey. “The message is not that it was not worth giving up because he got the disease anyway, but that the happiest years of his life were those once he stopped,” he said.
Mr Carr started smoking when he was 16 years old and within a few years had become a chain-smoker. In 1983 after making numerous failed attempts to quit he discovered a method that allowed to him stop smoking almost overnight.
His method urges smokers to lose their fear of a life without nicotine.
In 1985 he wrote The Easy Way to Stop Smoking. It quickly became the most successful book on stopping smoking with sales of more than three million. It has been translated into more than 20 languages.
Among his followers are comedian Ruby Wax, actor Anthony Hopkins and businessman Richard Branson. Mr Carr has over 50 clinics in 19 countries. He has also moved on to issuing advice on how to stop drinking and lose weight.
He claims that the success rate of clinics, where a session lasts around five hours and costs €295, has a 53% success rate after 12 months compared with 5% for those using willpower alone.