The presenter told Digital Spy that Arthur deserves to be successful as he possesses "a lot of talent" and "oozes...credibility".
"He was a great winner. I think he's a credible artist," O'Leary said. "I think we've got a chance with him to properly cultivate something, and I urge everyone to check your snobbery in at the door.
"He's a working class lad that's pulled himself up by his bootstraps, so you should give him a chance because he's got a lot of talent, and don't be snobby because he's come from a talent show.
"He does ooze that kind of angst and credibility, and also he's got a great sense of humour. He's a good guy."
O'Leary also suggested that Arthur could have his credibility boosted by teaming up with a few choice established artists.
"Obviously I don't have anything to do with how his career goes now," he said. "But if I was in charge of it, I'd get him collaborating with someone like Emeli Sandé or Labrinth or Tinie Tempah quite quickly.
"The first thing he should release post his winner's single should be a so-and-so featuring James Arthur."
Arthur's debut song 'Impossible' has become both the fastest-selling X Factor winner's single ever and the fastest-selling release of 2012.
Watch the video for James Arthur's 'Impossible' below: