Kennelly was born in Glenada, Oregon on April 15, 1912, and grew up in Glenada, Salt Lake City, Utah, and Albany, Oregon. She graduated from Albany High School and from Oregon State College in 1933. In 1940, she married Dr. Egon V. Ullman of Portland, Oregon; she was widowed in 1962. She lived for 40 years in downtown Portland where she held occasional salons and hosted diverse gatherings of selected guests.

Kennelly's writing career can be divided into three distinct periods:

• Improvement Era: 1930 - 1936
• Pulp romance: 1936 - 1940
• Novelist: 1949 - 1956

Improvement Era

Kennelly began her career at the age of 18 with the publication of three poems in Improvement Era in 1930. Between September of that year and January 1936, she published a total of 28 poems and five short stories in this The Church of Jesus Christ of Latter-day Saints (LDS) periodical. Although the majority of this work is considered sentimental and focused on love and romance, sub-themes appear as well, hinting at the insight into mature love, motherhood, death, and the restorative working of faith and nature (including human nature) that are expressed in The Peaceable Kingdom.

For the most part, Kennelly's Improvement Era work is considered naive and conventional in structure and plot. The poems are almost uniformly about romantic love. The stories typically end happily, but are varied in theme. How Lovely Youth focuses exclusively on young love; it concerns a young man returning from his two-year Church missionary work. Some Beautiful Way is about motherhood and step-motherhood, and the convergence of the internal realities of a little girl and her stepmother. And Afterward Came Spring is about death and a crisis of faith; given Kennelly's sub-themes in The Peaceable Kingdom, it's notable that in this story nature, rather than doctrine, brings about "proof" and resolution.

Fire and Song is, in the words of its author, "a story of faith". However, she states, "I'm nineteen. I tell you because I want you to understand if this tremendous theme is handled clumsily and a little too breathlessly."

Kennelly's remaining story, That Day Was Grand, 1935, is told from the point of view of a very young schoolgirl who idolizes a woman whom she considers the epitome of female beauty and perfection, and possessed of that ineffable quality of "cool." In the story, Kennelly reveals the character Rose's egotism, unattractive lifestyle and taste, slovenliness, shallow values and poor judgment, and her likely fate should she continue to walk the path she has chosen. Rose is not evil by any means (Kennelly does not appear to believe in human evil, or at least she never dwells on it), but she is dangerous to herself and dangerous to young Laurel through the influence she could so easily exert if not for the watchfulness and wisdom of Laurel's mother and grandmother. Rose's character is revealed through Laurel's words and the words of others as Laurel reports them.

Pulp romance

Kennelly's pulp career began the year her Improvement Era contributions ended, in 1936. This year saw the publication of her last poem in the Mormon periodical On A Restless Night, and one of her first mainstream stories, There's No Telling, for the pulp magazine All-Story Love Stories. She published a total of five romance short stories from 1936 to 1940 in All-Story Love Stories and Street & Smith's Love Story Magazine. The stories themselves are lost, unless surviving issues containing them can be located.) The poor paper quality that pulp periodicals are known for, combined with their age, yields a poor prognosis for success. However, it is possible to gain some idea of the nature of the periodicals themselves by viewing a few surviving examples of cover art for each magazine.

Novelist (1949 - 1956)

Kennelly's first novel, The Peaceable Kingdom, was published in 1949 and sold 500,000 copies. This was followed by four more, with the last published in 1956. These include The Spur (1951), a fictionalized treatment of John Wilkes Booth, and Good Morning Young Lady (1953), a coming of age novel, fictional but including anecdotes based on the life of Butch Cassidy.

Late career

Late in life Kennelly developed a second career as an artist, specializing in collages and mixed media constructions. She had two major exhibits. The first was at the Elizabeth Leach Gallery when Kennelly was 84 (approximately 1996), and the Mark Woolley gallery, in Portland, hosted an exhibit in 2000.

Toward the end of her life Kennelly moved to Vancouver to be near her sister, and died there in January 19, 2005 at the age of 92.