The much-loved broadcaster has become the latest big name star to part ways with the station, following in the footsteps of Graham Norton, Chris Evans and Vanessa Feltz.
Ken will be moving to rival station Greatest Hits Radio, and will take his long-running quiz PopMaster with him.
BBC Radio 2 broke the news of 71-year-old Ken's decision in a tweet this morning. The annoncement read: "We have some news… After 31 years of presenting the 9:30am-midday weekday show Ken Bruce has decided to leave.
"We’re going to miss you lots Ken and want to congratulate you on a fantastic career at the BBC."
The broadcaster also shared a statement from Ken as he revealed it was "time for a change".
He said: "After 45 years of broadcasting on BBC Radio it's time for a change.
"I would stress that this is entirely my decision. I will always be very proud of my association with the BBC and Radio 2".
Ken will present his final show at the end of March before moving to rival station Greatest Hits Radio just days later.
The Scotsman will take over from Mark Goodier in the 10am until 1pm weekday slot, with his new gig starting in April.
The radio DJ said of his new role: "What better way to celebrate my forty-five years in radio than with a new adventure and a brand-new show on Greatest Hits Radio.
"I say brand-new but there will still be PopMaster, me and my musings and all the great records you know and love from the 70s, 80s and 90s.
"I’m looking forward to getting started and to you joining me for my very first show. See you in April!"
Ken will kickstart a weekday line up that also includes presenters Simon Mayo at Drivetime and Jackie Brambles in the early evening.
Ben Cooper, Chief Content & Music Officer, Bauer Audio UK said: "Ken Bruce is a broadcasting legend, with the biggest radio show in the UK, so as well as today being an exciting announcement for Greatest Hits Radio and its growing audience, it is a hugely significant moment for the industry.
"What a fantastic start to a great year of increased ambition and innovation for Bauer Media Audio."
BBC Radio 2 has seen a series of stars leaving the radio channel in the last two years including Paul O'Grady, Steve Wright, Craig Charles and Vanessa Feltz.
A shakeup last year saw Steve Wright and Craig Charles' shows have been axed while Vanessa Feltz left and other presenters lost their slots.
While some have left the corporation entirely, others have continued to work for the BBC.
In September former BBC Radio DJ Simon Mayo – who suddenly left the station in 2017 – predicted there would be more exits.
He said: "I haven’t been in the building for four years so I don’t have any particular insights, other than that this stuff will continue to happen.
"My guess is there will be more in the next few months. That’s the direction the station is going in and they are prepared to lose the older listener."