Nick Hewer is quitting Countdown after nearly 10 years as host of the game show.
Announcing the news on Twitter, he said the coronavirus pandemic had prompted him to reconsider his future.
The former Apprentice star said he would not be renewing his contract for January as he approaches his 77th birthday and a decade on the Channel 4 programme.
He recently took a break from filming to shield from Covid-19 at home and was replaced by BBC Radio 5 Live presenter Colin Murray.
It is not yet clear who will take his seat on the long-running programme.
Writing on Twitter on Monday, Hewer said: “Delighted to be back in the Countdown studio after another enforced lockdown, BUT this latest lockdown has given me an opportunity to consider my future life and I’ve decided it’s a good time to step down at the end of my contract in the New Year.
“As someone in his 77th year, who will be in his 10th year hosting the great British institution that is Countdown, I think it’s time to smell the flowers and get a dog.
“But let me now take the opportunity to say that it’s been a privilege and a pleasure to take the helm of Countdown, first broadcast broadcast back in 1982 and still a Guinness record holder.”
He thanked Channel 4 and his “wonderfully talented” co-hosts Susie Dent and Rachel Riley among others.
The presenter also wished his successor luck, writing: “And so, to whoever takes my seat, I wish you every success and hope that you have as much fun and reward as I’ve enjoyed.”
Hewer previously announced in November that he would not be hosting Countdown while lockdown measures remained in place across the UK.
He joined the show, which debuted in 1982 and has seen multiple presenting line-ups, in 2012, taking over from sports presenter Jeff Stelling.
Formerly a public relations consultant, Hewer met ex-Amstrad owner Lord Sugar through work and eventually joined him as an adviser on The Apprentice on BBC One, launching a career on TV.
His former co-star and Apprentice boss, Lord Sugar, congratulated him on the news.
He tweeted: “Well done Nick. You work too hard and produced some good stuff for me and countdown. Good decision now enjoy yourself instead of driving up and down the motorway every week. All the best from Alan + Ann”.
Countdown presenter Rachel Riley was also among those responding to the news.
She tweeted: “Right, time to get a bingo list of things you need to slip into the show while you’re hosting @Nick_Hewer.”
Another of the show’s current stars, Susie Dent, tweeted: “The voice of a gentleman who will be dearly missed.”