The broadcaster, who previously presented Football Focus from 2009 to 2021, has hosted the morning show since 2016.
He will replace Sian Williams to present 5 News, after Williams announced she was stepping down earlier this month.
In a video shared on Twitter, Walker said it was a “massive decision” to leave Breakfast, adding: “I don’t think opportunities like this come round very often.”
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He had previously fronted Breakfast with Louise Minchin, who departed in September 2021.
She was replaced by Sally Nugent, whose appointment was announced the following month.
Walker said: “I have a little bit of news for you. In the next few weeks, I’m going to be leaving BBC Breakfast and moving to 5 News and to Channel 5.
“I’m really excited but this has also been a massive decision for me because I love BBC Breakfast, I love working alongside Sally and I love the team there."
He continued: “But Channel 5 came with big ambitions, with big plans and I don’t think opportunities like this come around very often and I can’t wait.
“I’ve also had the incredible privilege of working on some iconic programmes over the last few years, both at the BBC and elsewhere.
“And what I love about this deal is I not only get to present the news, but also host a whole range of new programmes right across the channel.
“And what an honour to step into the shoes of Sian Williams. I know how popular she is with both the team and also the audience, so all I can say is I will do my best to maintain her incredibly high standards.
“Thank you for watching and I’ll see you soon on a TV screen somewhere.”
Walker took part in the 2021 series of Strictly Come Dancing, revealing he signed up for the show to do something “fun” and have a “giggle” after reporting on difficult news stories during the pandemic.
Cait FitzSimons, editor of 5 News, said: “I’m hugely excited about Dan’s decision to join 5 News.
“We pride ourselves on the deep connection we have with our viewers across the country, and this is a key strength of Dan’s, helping secure his place as one of Britain’s best and most popular broadcasters."