Speaking at the premiere of One Direction: This Is Us, the popular host was quizzed on speculation that Simon Cowell may be considering a return to the UK panel.
"If Simon [Cowell] comes back, the dynamic would be very different.Gary wouldn't be there - he'll be leaving at the end of this year," he told reporters.
O'Leary even threw his own hat into the ring, saying, "I'd love to judge. I'd be so strict. I'd be nice and strict."
Gary Barlow has yet to confirm his plans for the coming years on X-Factor, though it is believed he is ready to return to song-writing and working with Take That, and O'Leary's remarks appear to confirm that.
A spokesman for the show said: "We are currently focusing on the forthcoming 10th series, and no decisions will be made on next year's judging panel line-up until further down the line."
This week, ITV confirmed that the show will return on Saturday August 31, at 8pm, while reports suggest a new style of voting will come into play this year. A 200-second flash vote is being considered, with the contestant with the lowest number automatically put into the bottom two.
A source said: "This year's X Factor features a number of changes across the series including our brand new audition format.
It's too early to confirm changes to the live shows but the flash vote on Saturday is something being considered to add more drama to the show."
Along with head judge Gary Barlow, this year's judging panel features Nicole Scherzinger, Louis Walsh and Sharon Osbourne, who replaced Tulisa Contostavlos.
"It's a good panel this year. There's no bitchiness to it, but they wind each other up," said O'Leary. "Sharon's brilliant. Having Sharon back, she has just been a revelation, she really has. I hope she stays."
Gary Barlow Arriving For X Factor Auditions In Cardiff