Welsh, 62, says he is paid even when his novels are stolen from shops - because the stores have to cover the cost to publishers.
The author wrote Trainspotting 1993 and it went on to become a major British film starring Ewan McGregor and Kelly Macdonald.
It is a story about a group of heroin addicts in Edinburgh and the novel is often cited as the most shoplifted book in Britain.
But Welsh says people nicking copies of his novels Trainspotting, The Acid House, Filth, and Porno is ''brilliant'' - because he still gets royalties.
He revealed the financial loophole on the podcast Midnight Meets with Colin Murray.
Speaking about Trainspotting, Welsh said: ''It is a source of pride that people kinda nick it.
''I always get some wee yob that comes up to me and goes, 'I got your books, I stole them all'.
''I say 'well, look, I appreciate that because they usually go to the book sellers on a sale or return basis.
''So if they don't sell the bookseller can't return them to the publisher.
"That means I get my royalties.
''So I appreciate you stealing them because it means double sure that I get paid. Fabulous. It's brilliant. It's unbeatable.''
Released in 1996, the first Trainspotting film opens with an iconic scene in which the main characters are seen sprinting down Edinburgh’s Princes Street – ironically having shoplifted items from a store.