Her family confirmed she died peacefully at home in the early hours of this morning.
Bland was a familiar voice on Radio 5 Live as a newsreader and presenter, and won praise for co-hosting You, Me and the Big C, a podcast about cancer.
She has also documented her battle with the disease on an award-winning blog.
Following the announcement, Rachael's husband, Steve said in a statement: "She was an incredibly talented broadcaster as well as a wonderful and much loved daughter, sister, aunt, niece, wife and, most importantly to her, a mother to her precious little Freddie."
"We all take such huge comfort and pride from the amazing and tireless work she has done since her diagnosis to reduce the stigma around cancer and prove that it is possible to live life to the fullest even when facing huge challenges on a daily basis. At the end, even though her body was at its weakest, her voice was at its strongest and most powerful.
He describes her as "perfect in every way", adding "we will miss her more than words can say".
In August, the Cardiff-born broadcaster said she was writing a memoir to leave for her two-year-old son Freddie as a "love letter to my beautiful boy".
She began her BBC career more than 15 years ago as Rachael Hodges and married fellow BBC journalist Steve Bland in 2013.
As well as appearing on 5 live, she worked as a news presenter on the BBC News Channel, BBC World and BBC North West Tonight.
She was diagnosed with primary triple-negative breast cancer in November 2016 after finding a lump under her arm.
The presenter began chemotherapy just after Christmas that year, had a mastectomy the following July and went into an immunotherapy clinical trial this May, but the cancer had spread too far for her to stay on that treatment.
Throughout her battle, she earned admiration for her dignified and positive outlook, and for her efforts to give an honest portrayal of cancer on her podcast - with the tagline "Putting the CAN in cancer" - and her blog, titled Big C Little Me.
Rachael presented the podcast with fellow cancer sufferers Lauren Mahon and Deborah James. They spoke to celebrity guests and addressed practical matters including hair loss, tips for dealing with finances and telling your nearest and dearest.
The podcast reached number one on the iTunes chart on Tuesday - an ambition of Bland's, which her husband tweeted had made her "very happy".
"The whole sharing process has been very cathartic," Rachael wrote in an online article earlier this month. "It's been a real support to know that people have found them so helpful through their treatment, but in a selfish way they've helped me just as much."
But the 40-year old also frequently spoke about how her biggest fear was leaving Freddie without a mother.
"I'm not scared of dying," she wrote in The Daily Telegraph in August. "I only fear for those I leave behind. For my darling Freddie... for Steve and our families."
She added: "Steve and I don't discuss how he'll cope without me, but we do talk about all the things I want him to do with Freddie when I'm gone.
"He's quite an emotional man, so I know he'll do a lot of crying. But he is also the most amazing father and will keep going and stay strong for our son's sake."
Bland said she was looking for a publisher for her memoir, which she described as "my love letter to my beautiful boy that I hope will leave the imprint of me and my love for him around him forever".
In her article published on The Huffington Post, Bland revealed that the book was almost finished. She also said she was wrapping presents for her son to open on every birthday until he's 21.
"Personal effects like my notepads - so he can see what my writing was like. Or the perfume he helped pick out for me earlier this year so he'll remember my smell." SHARE THIS STORY USING ANY OF THE BUTTON BELOW ⬇ PLACE YOUR TEXT ADVERT BELOW ⬇⬇⬇