The 52-year-old TV presenter - who has worked on the BBC morning show since 2002 - made the announcement live on the show alongside co-presenter Dan Walker, admitting she is ready to give up early mornings and will be stepping down later this year.
Minchin told viewers: "Let me take a deep breath, everybody there is something I want to tell you about.
"It will be this year 20 years since I first presented this programme.
"Since then I've felt part of a huge, enormous BBC Breakfast family which includes everyone who works here, everyone on the team and every one of you who watches the programme.
"I've loved being part of it but - there is a but - I've decided that is time that I stop setting my alarm for 3.40am - sometimes if I'm feeling really rebellious 3.46am - in the morning and I'm going to be leaving the programme.
"It's not going to be for a while. But before anything else I wanted to thank everyone that is watching for your loyalty and your support over all those years.
"I have absolutely loved being part of it and I will really miss it, but it's time now to stop that alarm early in the morning.
"And thank you for watching for all these years."
The British journalist - who was born in Hong Kong where her army major father was serving at the time - studied journalism at the London College of Communications and also hosted the BBC News at One between 2006 and 2012.
Walker, 44, paid tribute to his co-anchor, tweeting: "As with everything she does... Louise announces her departure from the show with dignity and class. We will all miss her enormously at #BBCBreakfast. She is not only wonderful at her job... she is a great friend. Enjoy your lie-ins @louiseminchin."
Amateur triathlete Minchin - who has guest-hosted The One Show and was runner-up on Celebrity MasterChef in 2016 - revealed back in 2019 that she struggled with negative comments from online trolls.
Minchin wrote in Cheshire Life magazine: “You might think I am oversensitive (I probably am), and need to grow a thicker skin (I probably do), but the truth is I can read a hundred nice comments about me but it will be the nasty one I will remember, try as I might to shrug it off."
The news presenter married her husband in 1998 and they have two daughters together.