Cleary was born in McMinnville, Oregon, the only child of Chester Lloyd Bunn and Mabel Atlee. Her great-grandfather was Jacob Hawn (Haun) of Haun's Mill. Spending her earliest years on a small farm, Atlee felt that this was a disadvantage for the students at the small farm school, and she made arrangements to have books sent there from the state library. As a result, Cleary grew to love books.

When Cleary was six years old, her family left the farm and moved to Portland, Oregon, where she attended elementary and high school. She blamed her struggle with reading in this new school setting partly on her dissatisfaction with the books she was required to read and partly on an unpleasant first-grade teacher. Also, after six years of living in the country, on a farm, the city life in Portland took a toll on her health, and she was frequently ill, which set back her schoolwork and reading skills further.

In the second grade, Cleary studied under her favorite teacher, and by the third grade, she had greatly improved her reading ability and found new joy in books. She read The Dutch Twins by Lucy Fitch Perkins, and became a frequent visitor to the library. As a child her favorite book was Dandelion Cottage by Caroll Watson Rankin.

The grammar school librarian was largely responsible for developing her love of reading. She encouraged Cleary to check out books about subjects to which she could relate. The librarian not only encouraged her to read but also to write her own books, and instilled in her the belief that she, too, could write for children some day.

In 1934, age 18, Cleary moved to Ontario, California, to attend Chaffey College, from which she earned an Associate of Arts degree. She worked as a substitute librarian at the Ontario City Library. After graduating with a BA in English in 1938 from the University of California at Berkeley, she studied at the School of Librarianship at the University of Washington in Seattle, where she earned a degree in library science in 1939.

Because attending college during the Great Depression was expensive, Cleary worked through the university's cooperative education program to earn money. One afternoon, during a break from her chores at work, she found herself having a sandwich with a young gentleman named Clarence Cleary, her future husband.

The library science degree allowed her to work with young children and develop relationships with them at all socioeconomic levels. Her first full-time job as a librarian was in Yakima, Washington, where she met many children who were searching for the same books that she had always hoped to find as a child herself. Cleary sympathized with children who felt that there were no books written about children like themselves. Their pleas convinced her to help provide children with stories to which they could relate.

In response to this experience, she later wrote her first book, Henry Huggins, which was published in 1950. It was about a boy, his dog and their friends, all of who lived on Klickitat Street in Portland (the street only a few blocks from where Cleary grew up as a child). According to Cleary, Henry Huggins and his friends represented all the children she grew up with, and the ones who sat in front of her during library story hours.

As she crafted her first book, she recalled advice from her mother and incorporated her beliefs that the best writing was simple and filled with humor. She also remembered advice from a college professor who emphasized writing about universal human experience. Beezus and Ramona, Cleary's first book to center the Quimby sisters around a story, was published in 1955, although Beezus and Ramona made frequent appearances in the Henry Huggins series as supporting characters.

The opportunity to work with children as a librarian opened new doors for Cleary. She wanted to write books for children but was unsure if she had the experiences needed to write what she wanted. A publisher wanted her to write a book about a kindergarten student. Cleary felt that she could not write about this because she had not attended kindergarten. She later changed her mind after the birth of her twins. She learned to add a little wit and charm to her writing for children, with the hope that it would spark an interest in reading among her students and encourage them to read more books like it. She is now an international favorite among children’s authors.

In 1940 she married Clarence T. Cleary, and they moved to Oakland, California. They eloped because Cleary's parents were Presbyterians and did not approve of the union even after it occurred because he was Roman Catholic. They had twins, Marrienne Elizabeth and Malcolm James. Clarence Cleary died in 2004. Beverly Cleary currently lives in Carmel, California. She is still writing.

She has also written two autobiographies, A Girl from Yamhill and My Own Two Feet.

Cleary’s books have been published in 15 different languages and have earned many awards. A few examples of awards she has won include a Newbery Medal for Dear Mr. Henshaw (1984); a Newbery Honor for Ramona and Her Father (1978 ); a Newbery Honor for Ramona Quimby, Age 8 (1982); a Laura Ingalls Wilder Award from the Association for Library Services to Children of the American Library Association (1975); the Catholic Library Association's Regina Medal (1980); and the Children's Book Council's Every Child Award (1985). Cleary’s books have been read on PBS and ABC-TV. She received the Library of Congress Living Legends award in the Writers and Artists category in April 2000 for her significant contributions to the cultural heritage of the United States. She received the National Medal of Arts in 2003.

Her birthday, April 12th, is recognized as National Drop Everything and Read (D.E.A.R.) Day, in promotion of sustained silent reading.

In Portland, Oregon, the Hollywood branch of the Multnomah County Library, near where she lived as a child, commissioned a map of Henry Huggins's Klickitat Street neighborhood that resides on its lobby wall. Statues of her beloved characters Henry Huggins; the Huggins's dog, Ribsy; and Ramona Quimby can be found in Portland's Grant Park. In June 2008, the two-campus K—8 school of the same neighborhood, Hollyrood-Fernwood, was officially renamed Beverly Cleary School. As a child, Cleary attended the former Fernwood Grammar School, one of the two buildings that makes up the school that now bears her name.

In 2004, the University of Washington Information School completed fund-raising for the Beverly Cleary Endowed Chair for Children and Youth Services to honor her work and commitment to librarianship. In 2008, the school announced that she had been selected as the next recipient of the University's Alumnus Summa Laude Dignatus Award, the highest honor that the University of Washington can bestow on a graduate.

Cleary has a 220-student residential hall at the University of California, Berkeley named after her.

Cleary has been mentioned as a major influence by other authors, including Laurie Halse Anderson, Judy Blume, Lauren Myracle and Jon Scieszka.

• Henry Huggins - (1950)
• Ellen Tebbits - (1951)
• Henry and Beezus - (1952)
• Otis Spofford - (1953)
• Henry and Ribsy - (1954)
• Beezus and Ramona - (1955)
• Fifteen - (1956)
• Henry and the Paper Route - (1957)
• The Luckiest Girl - (1958)
• Jean and Johnny - (1959)
• The Hullabaloo ABC - (1960)
• The Real Hole - (1960)
• Leave it to Beaver - (1960)
• Beaver and Wally - (1960)
• Here's Beaver! - (1961)
• Two Dog Biscuits - (1961)
• Emily's Runaway Imagination - (1961)
• Henry and the Clubhouse - (1962)
• Sister of the Bride - (1963)
• Ribsy - (1964)
• The Mouse and the Motorcycle - (1965)

• The Growing-Up Feet - (1967)
• Mitch and Amy - (1967)
• Ramona the Pest - (1968)
• Runaway Ralph - (1970)
• Socks - (1973)
• Ramona the Brave - (1975)
• Ramona and Her Father - (1977)
• Ramona and Her Mother - (1979)
• Ramona Quimby, Age 8 - (1981)
• Ralph S. Mouse - (1982)
• Dear Mr. Henshaw - (1983)
• Ramona Forever - (1984)
• The Ramona Quimby Diary - (1984)
• Lucky Chuck - (1984)
• Janet's Thingamajigs - (1987)
• A Girl from Yamhill - (1988)
• Muggie Maggie - (1990)
• Strider - (1991)
• Petey's Bedtime Story - (1993)
• My Own Two Feet - (1995)
• Ramona's World - (1999)