According to Andrew Crofts it is possible, but only if you 'play the game' right by doing a balancing act, so to speak. By that I mean ... well, why don't you read the article he wrote which will clarify that point. It was posted on the theguardian.com in January this year, addressing that very issue all aspiring writers want to know: Can I Make A Living As A Writer?
Earning a living as a writer is as likely as winning the lottery. Instead of writing books and persuading others to buy them, find out what people want to write, then do it for them
If you are seriously thinking about embarking on a writing career, may I suggest you read his article first. Find out all about the man - his dreams, his ambitions as a young lad - what he initially had to do to begin earning money by writing, and how he eventually reached a point where is quite content and comfortable with his earnings as a paid writer.
However, the vast majority of the money he earned from his writing over the course of forty years did NOT come from royalties from his books, which by the way became bestesellers. So be prepared for some harsh realities...it was never an easy road that he travelled...