Julie, 46, played transgender Hayley for 16 years but was initially only supposed to be on the show for a few episodes.
"I wasn't meant to be in Coronation Street for any longer than two weeks," Julie told the Sunday Telegraph's Stella magazine.
"The character of Hayley was originally written as a joke. It wasn't a politically correct one, but this was back in 1998. The joke was that Roy Cropper [played by David Neilson] was going to go on a series of disastrous blind dates, one of them being with a man who had transgendered to a woman."
Hayley, who was born Harold Patterson, became the first transgender character to appear on a British serial TV show.
Coronation Street's first transgender character Hayley Cropper was originally written in as a joke
Coronation Street fans were devastated when Hayley died
Hayley was originally written as a joke
Viewers fell in love with Julie's portrayal of the factory worker and she became one of Coronation Street's most popular characters.
Julie, who is a patron of the charity Trans Media Watch, said getting people to accept Hayley for who she was important for her when she took on the job.
She added: "To me, that was it. You make people like this woman – understand her – and you say more than any political speech or lobbying."
Coronation Street: Julie said she was determined to make the character a success
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Coronation Street's most dramatic moments
Thu, January 12, 2017
Coronation Street's most dramatic moments.
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Michelle Connor suffered a heartbreaking miscarriage
Julie won six awards during her time on the Cobbles and left fans devastated when she left.
Hayley was involved in a distressing assisted suicide storyline after she was diagnosed with terminal pancreatic cancer in 2014.
Julie, whose credits also include Cucumber and Happy Valley, will be seen later this year in the new series of Broadchurch.
Coronation Street continues tomorrow night at 7.30pm on ITV.