She grew up in Springfield, Ohio. Her father, a Prussian immigrant, was a Lutheran clergyman. Her mother, a native of Franklin County, Ohio, was a schoolteacher before her marriage.The Lenskis had five children, three girls and two boys, of which Lois was their fourth child.In 1899, Pastor Richard Lenski was called to serve a parish in Anna, Ohio, and the family moved to the small rural community west of Springfield.The next twelve years of Lois Lenski's life were spent in Anna, and many of her fondest childhood memories were of life in this small town.Lenski's autobiography, Journey Into Childhood, provides a detailed description of her years in Anna. Although a strict father and a busy pastor, Richard Lenski always made time for his children and involved them in his hobbies of drawing and photography. Marietta Lenski was a devoted mother and homemaker who encouraged her children to work hard and pursue a college education. Lois Lenski's home life instilled in her the importance of learning. In addition to being an avid reader, she was also skilled at sewing and drawing, often copying pictures from books and magazines.

Since Anna, Ohio was too small a community to offer secondary education, Lois Lenski made a daily train trip to Sidney, Ohio to attend high school.She graduated in 1911 and the family moved to Columbus, where her father joined the faculty at Capital University.Since her father's institution was not co-educational, Lenski enrolled at Ohio State University.Following in her mother's footsteps, she prepared for a career in teaching.In addition to education courses, she took as many art courses as possible, primarily drawing and lettering.In 1915, Lois Lenski graduated with a Bachelor of Science degree in education and a teaching certificate.Although Richard and Marietta Lenski assumed their daughter would settle into a teaching job, Lois chose to deviate from her parent's wishes. At the urging of her art professors from Ohio State, she moved to New York City to study at the Art Students League of New York.

For the next four years, Lenski took art courses and worked part time to support herself. Although existing on a shoestring budget, Lenski loved the cultural advantages of New York. She took advantage of the opportunities to develop her talent through her classes and part time jobs such as lettering and painting greeting cards or drawing for fashion advertisements. In her class on illustration Lenski first met Arthur Covey. She soon became his assistant in painting a number of murals. In October 1920, Lenski traveled to London and Italy to study and work. It was during her months in London that Lenski was first hired to illustrate books for the publisher John Lane.

In 1921, shortly after returning from her travels, Lenski married Arthur Covey. She became thereby a stepmother to his two children, Margaret, age 12 and Laird, age 4. With her additional household and family responsibilities, Lenski had to carve out time for her own work. This often proved a difficult task and Lenski received no help with household chores from her new husband.

Lenski described the 1920s as her years of apprenticeship. Through continued practice and additional art classes, Lenski developed her talent in human figures and landscape drawing. She spent much of her early career as an illustrator of children's books. When a publisher suggested that she write her own story to accompany her drawings, Lenski embarked on a new track in her career. Although she had never considered writing, Lenski was determined to try her hand at being an author and illustrator. In 1927 Lenski published her first book, Skipping Village. The following year she wrote her second book, A Little Girl of 1900, based on her childhood experiences.

In February 1929, Lois Lenski gave birth to her son, Stephen. Within a few months the newly expanded Covey family moved to a farm in Connecticut that would be their home for over 30 years. Spurred by Stephen's toddler years, Lenski began her "Mr. Small" series with The Little Family (1932) and The Little Auto (1934). In the early stages of her writing in the 1930s Lenski wrote "a group of imaginative stories for pure amusement." These included Grandmother Tippytoe, Arabella and Her Aunts and Benny and His Penny. Lenski next moved into historical fiction, beginning with Phebe Fairchild, Her Book (1936), a story based on the Lenski farmhouse in Connecticut, built in 1790. Over the next decade Lenski wrote six more historical books including Bound Girl of Cobble Hill (1938), Blueberry Corners (1940) and Indian Captive (1941). Phebe Fairchild and Indian Captive both were named Newbery Honor books. As a change of pace from her intensely researched historical books, Lenski also published picture books including Sugarplum House (1934) and Gooseberry Garden (1935). She continued to illustrate the works of other writers, most notably Maud Hart Lovelace's first four Betsy Tacy books. She worked very closely with Lovelace and her publishers to make the books true to their real-life context.

During the 1940s two other major factors, her travels and her grandson, influenced Lois Lenski's writing. Due to poor health, Lenski was ordered by her physician to get away from the fierce Connecticut winters. She and Arthur Covey chose to spend winters in the South, first in Louisiana and then in Florida. It was during her travels that Lenski began research and writing on her series of regional books. Beginning with Bayou Suzette (1943), based on life in the Louisiana backcountry, Lenski wrote some 16 regional books over the next twenty years. Perhaps her most successful regional story was Strawberry Girl (1945), winner of the Newbery Medal in 1946.

Inspired by her grandson, David Chisholm, Margaret's son, Lenski began the "Davy" series of books in the mid-1940s. David lived with his grandparents during the summers of 1943-1945 and was initially a very difficult child. Lenski's grandmotherly kindness finally won him over and his childhood activities became the basis for a series of six picture books including Davy's Day (1943) and A Surprise for Davy (1947).

In the 1950s and early 1960s, Lenski published the Roundabout series, also based on various areas of the U. S., but written for somewhat younger children. Much like the regional series, the Roundabout books explore the geographically and culturally diverse lives of children from peanut farms (Peanuts for Billy Ben, 1952), to cranberry bogs (Berries in the Scoop, 1956) and from housing projects (Project Boy, 1954) to Indian reservations (Little Sioux Girl, 1968).

Although Lenski suffered from illness again in the early 1950s, she gradually recovered and resumed her writing. Lenski and her husband began to spend half the year in Florida and built a house there in 1951. Arthur Covey, a man blessed with near perfect health all his life, became seriously ill in 1958. Although he resumed sketching and painting in their Florida home, he succumbed to his illness in February 1960. Lenski eventually sold the Greenacres farm in Connecticut and made her home in Florida year round. She continued writing in her later years, publishing her autobiography in 1972. In September 1974 at 80 years of age, Lois Lenski died at her home in Florida.

Lenski's many books have become classics in children's literature. Her books depicted children's lives much more realistically than other children's authors. She enthusiastically tackled areas and subjects long neglected in writing for children. The popularity of her works and their distribution in other languages are testimony both to her skill as a writer and to her continuing appeal to children.

Her impact on children continues through the Lois Lensky Covey Foundation, a charitable institute whose purpose is to assist organizations in their efforts to provide books to children who might otherwise lack access to children's literature.

Her papers are held at University of California, Berkeley, and University of North Carolina, Greensboro.