The broadcaster became a trainee with the broadcaster in 1994 and is now one of its most well-known sports presenters.
"I wanted to change the way people think - to have an impact," Balding told Reader's Digest
"Then I met [BBC horse riding correspondent] Cornelius Lysaght and he said, 'Would you like to come for a voice test for radio?'
"I'd done a lot of debating, but I hadn't thought of radio as a medium for me, and there weren't many women in sports broadcasting at the time. But I was very naïve. I'm not sure I even realised that I was doing something unusual."
She added: "I freelanced for Cornelius for what was Radio 5 then. It became 5 Live on April 1, 1994, and I started as a trainee that day.
"They were looking to make a new kind of sports reporter to suit 5 Live, so they put me on the traineeship to try and achieve that; I don't know whether they succeeded!"
Balding continued: "They got me presenting football, rugby - everything.
"My first broadcast was from Highbury; Arsenal were parading in 1994 when they won the [Cup] Winners' Cup. I did vox pops in the street.
"It was a very alien environment for me; I didn't know much about football or Arsenal. But I loved people's passion for the club. I thought, 'This really matters to people'."
The full interview with Clare Balding appears in the February issue of Reader's Digest, out January 22.