Minchin first appeared on the programme in 2001, and went on to replace Sian Williams as a full-time member of the team when the show moved from London to Salford in 2012.
This is everything you need to know.
What did she say?
On 8 June, Minchin appeared on BBC Breakfast where she confirmed the news.
She said: “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 watched the programme.
“I’ve loved being part of it, but - and there is a but - I have decided that it is time that I stopped setting my alarm for 3:40 - sometimes when I’m feeling very rebellious 3:46 in the morning - and I’m going to be leaving the programme.
“It’s not going to be for a while, and just before anything else I wanted to thank everybody who’s watching for your loyalty and support over all these years. I have absolutely loved being part of it. I will really miss it.
“But it is time now to stop that alarm early in the morning, and thank you for watching all these years as well.”
In a BBC statement, Minchin added that there are “so many memories” that she will be taking with her after she leaves the show.
She said: “I will take so many memories with me, including reporting on the shock and anguish of the Manchester Arena bombing, starting a national conversation about menopause, and the life changing moment I took part in the Breakfast Christmas Cycling Challenge which inspired my ongoing passion for endurance sport, which I will continue when I leave.
“A big thank you to everyone who has watched and supported me, I have loved it and I will miss you all.”
When will she be leaving - and what will she do next?
During her announcement, Minchin said that she will be departing “sometime after the summer” and that the date “is not set in stone”.
She said that after she leaves the programme that she will be continuing her passion for endurance sport, and also revealed other projects that she plans to pursue.
She said: “I’ve got lots of really exciting adventures planned. I’m trying to write a book about that as well.
“And I’ll continue my podcast, which is all about the mental and physical benefits of sport and exercise.”
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What has her co-host Dan Walker said?
Minchin’s regular co-host, Dan Walker, said: “From a personal perspective, my life will be a lot poorer without you.
“You are not only a star, you are fantastic at your job, you’re brilliant to work with but you’re also a great friend.”
Walker also Tweeted: “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.”
Walker posted a series of pictures of himself and Minchin, writing: “This feels like a break-up. What am I going to do without Louise?
“Thank you for all the lovely messages after an emotional morning on #BBCBreakfast - I’m sure Louise will get to read them all later. My life will be poorer without her on the sofa. She’s the best.”
What did Stephen Graham say?
Actor Stephen Graham was among the guests on the show when Minchin announced her departure.
Graham, who is currently starring in the BBC One drama Time, joined the BBC Breakfast studio via video call.
He said: “Louise, I am devastated you are leaving by the way. Honest to god. You have been a stalwart for the last 20 years.
“It has been lovely waking up with you in the morning and receiving our news from you.
“You are a consummate professional and you are amazing at your job. You are wonderful. You brighten up the day.”
Who will replace her on BBC Breakfast?
Currently there is no word about who might replace the BBC Breakfast host on the show.
Having only just announced her departure, and with no set date for leaving, there has been no announcements about any possible replacements for Minchin.
Dan Walker, Naga Munchetty and Charlie Sayt are among the current team of presenters on the early morning show.
BBC Breakfast editor, Richard Frediani, said: “Millions of viewers have regularly woken up with Louise for 20 years and welcomed her and BBC Breakfast into their homes.
“We will miss her brilliant journalism, good humour and boundless energy. She has been a tremendous BBC Breakfast colleague on and off screen, and will always be a friend to the team.”