Stelling, who has presented the programme since January 2009, is leaving the show to focus on his career as a sports presenter.
"I'll give you a little world exclusive," Stelling told Tenerife's Oasis FM yesterday. "Because I'm doing the Champions League for Sky next season I've actually resigned from Countdown and I'll be finishing at the end of December.
"You've got to really have your priorities and my priority is football. I love it, and Soccer Saturday, so I've committed myself very much to that next season."
Stelling presented the show alongside co-host Rachel Riley, who took over from Carol Vorderman in 2009.
On saying goodbye to Riley, Stelling added: "That'll be really, really sad. We've had some great times and I'll miss her."
A spokesperson for Channel 4 confirmed that the network has already begun the search for a new presenter.
"Jeff will continue to present Countdown until the end of the year," the spokesperson said. "He's had a brilliant three years on the show and we're sad to see him go."
They added: "We're already talking to a number of people to find a replacement."
Countdown airs weekdays on Channel 4.