The author told how he will meet with Oscar-winning director Danny Boyle, screenwriter John Hodge and producer Andrew Macdonald at the end of the summer to discuss the plot for a new movie.
The Edinburgh-born writer said the box office success of sequel T2 Trainspotting, based on his book Porno, meant movie bosses were keen for a third instalment.
Welsh, 58, said he will publish a new novel in March next year which will reunite the Trainspotting characters and could form the basis for the next film.
His Trainspotting prequel novel Skagboys is also set to be turned into a television series.
He said: “I have got a new book coming out in March which a lot of people will say would be the basis of a third Trainspotting movie, but we will kind of see how that goes.
“Something we plan to do at the end of the summer is to get everyone back together and have a chat about where to go.
“We have Skagboys optioned now as a TV series, and I’m doing another project with Sony, but they made quite a bit of money out of T2 and that tends to concentrate the mind.
“I do think that anything that happens Trainspotting-wise has got to involve all of us. That is why it took so long.
“I could have sold the rights to Porno to loads of different people but I kind of felt that it is that team, these four guys and the four main actors. You don’t want anyone else getting involved in it.”
T2 Trainspotting, the follow up to the 1996 film, saw Ewan McGregor’s character Mark Renton return to Edinburgh to meet up with old pals Sick Boy, played by Jonny Lee Miller, and Ewen Bremner’s Spud.
He embarks on a business deal with Sick Boy but soon finds himself being pursued by Begbie, played by Robert Carlyle, who has escaped from prison.
Fans flocked to the cinema to see the film which has made more than £30 million at the box office.
It had third biggest weekend opening of all time for an 18-rated film, behind only Fifty Shades Of Grey and Hannibal, and fourth-biggest 18-rated opening overall behind Legend as well.
The cast spent more than two months filming in various locations around Scotland, including Edinburgh, Glasgow, Bellshill in Lanarkshire and Blackburn in West Lothian.
Welsh has written a play called Performers which is set to be staged at the Edinburgh Festival next month.
A former heroin user, the author said he was surprised to still be alive as he approaches 60.
He said: “I expected to be dead by 30, so it’s something of an embarrassment to still be alive at 60, I suppose there is still time to kill myself.
“I did not expect to still be doing what I’m doing — it is weird after all these years that people are still reading the books and watching the films and taking an interest and hopefully buying tickets for the play at the festival.”