Her charity, the Doris Day Animal Foundation, confirmed the news, saying that she passed away early this morning at her home in California, surrounded by friends.
Though she had been in good health for someone her age, Day recently contracted a serious bout of pneumonia.
Day started her career as a singer, eventually appearing to sing in films like Love Me or Leave Me and Hitchcock's The Man Who Knew Too Much.
Day later became known for her portrayal of wholesome, innocent characters in romantic comedies like Pillow Talk and That Touch of Mink, though her 1976 autobiography stood in contrast to her clean-cut image.
She acknowledged her "unfortunate reputation of being Miss Goody Two-Shoes and America's Virgin," but opened up about her financial troubles, three failed marriages, and admitted that, "I staunchly believe no two people should get married until they have lived together."
Day never won an Academy Award, though she did receive honours like a U.S. Presidential Medal of Freedom and a lifetime achievement award from the Los Angeles Film Critic Association.
She retired from show business in the 1980s and devoted much of her time to her Doris Day Animal Foundation.
Read a selection of social media tributes to Day below.
RIP Doris Day pic.twitter.com/zPHtr9h4Yk— Cole Escola (@ColeEscola) May 13, 2019
The one, the only, the woman who inspired so much of what I do... Doris Day I love you, my calamity Jane. An iconic woman who I was hugely honoured to meet and share precious moments with. Rest in peace x pic.twitter.com/brkli7fKYE— Stella McCartney (@StellaMcCartney) May 13, 2019
One of my all time favourite stars has joined the heavenly choir. Rest in Peace the great & inimitable Doris Day. The last star of the Hollywood Golden Age. We'll bid you farewell by the Light of The Silvery Moon, but you will always be Young at Heart to us forever. 😢❤️ pic.twitter.com/VN0PUJAfnr— Elaine Paige (@elaine_paige) May 13, 2019
RIP to the one, the only Doris Day. pic.twitter.com/01rV9D7bq9— edgarwright (@edgarwright) May 13, 2019
Condolences to the family of Doris Day. She was the World's Sweetheart and beloved by all. ❤️ Que Será, Será!😞— William Shatner (@WilliamShatner) May 13, 2019
Remembering the legendary Doris Day. pic.twitter.com/DGITJc2woz— Warner Bros. UK (@WarnerBrosUK) May 13, 2019
RIP Doris Day. I'm sure she's happy to hang out with Rock Hudson again. pic.twitter.com/N3j9wVZCDb— 🏳️🌈 Ms. Marya E. Gates (@oldfilmsflicker) May 13, 2019
No matter how old you are, it's the music and movies of your youth that forever stir you. Kudos to Doris Day for the smiles she gave, the happiness she inspired and a life well lived. May her spirit soar.— Marianne Williamson (@marwilliamson) May 13, 2019
God Bless Doris Day! x What a voice. What a legend. R.I.P. https://t.co/87vYpO1NOm— Boy George (@BoyGeorge) May 13, 2019
We've lost another great Hollywood talent. Take a minute to appreciate the legendary Doris Day: https://t.co/72ssvivryz— Seth MacFarlane (@SethMacFarlane) May 13, 2019