The 1996 film reunited McGregor with Shallow Grave director Danny Boyle and proved a breakthrough moment in both their careers.
McGregor told The Big Issue: "When I made Trainspotting I didn't think - this is me, this is my moment.
"But I did have really amazing feelings about the film. I thought the book was fantastic and really captured the spirit of the country. I knew Danny was the best director to do it. And we had this perfect cast."
He added: "So I had really, really high expectations of it. But I couldn't have imagined... I remember seeing it for the first time, in London with my wife and my uncle, and coming out numb and shaky. It was so extraordinary.
"But I already had very strong self-belief so I didn't feel it would boost me particularly. Now of course I see it did. It became a global film and put me right in the public eye."
McGregor and Boyle worked together again on 1997's A Life Less Ordinary and could reunite for Porno, a sequel to Trainspotting based on author Irvine Welsh's follow-up novel.
However, in 2010, McGregor said that a Trainspotting sequel would not be filmed in the near future and later appeared to rule himself out of appearing in it.
Kelly Macdonald has claimed that Boyle told her her character Diane does not feature in his plans for the sequel.
Watch the Trainspotting trailer below: