Marion was born Marion Benson Owens in San Francisco, California, to Minnie Benson and Len Douglas Owens, an advertising and billboard executive ("billposter"),[3][4][5][6][7][8][9][10] later, developer of Aetna Springs Resort, Aetna Springs, Pope Valley, California.

Later she worked for Western Pacific Railroad as a commercial artist, then, at 19, as a "cub"[26][27] reporter for the San Francisco Examiner.

After moving to Los Angeles, in 1912,[28] Marion worked as a poster artist for the Morosco Theater[29][30][31][32] as well as an advertising firm doing commercial layouts.

Marion accepted, and began working on scenarios for films like Fanchon the Cricket, Little Pal, and Rags.

[33] Marion, having traveled from Los Angeles to New York for The Foundling's premiere, applied for work as a writer at World Films and was hired for an unpaid two-week trial.

She left in 1917 when, following the success of The Poor Little Rich Girl, Famous Players–Lasky signed her to a $50,000 a year contract as Mary Pickford's official scenarioist.

[37][38] She documented women's contribution to the war effort on the front lines, and was the first woman to cross the Rhine after the armistice.

[39] Upon Marion's return from Europe in 1919, William Randolph Hearst offered her $2,000 a week to write scenarios for his Cosmopolitan Productions.

[18][47] On October 23, 1915, Marion participated in a parade of more than thirty thousand supporters of women's suffrage in New York City.

[52][53] In early December 1928, Thomson stepped on a nail while working in his stables, contracting tetanus, and died in Los Angeles on Christmas Day 1928.

She had two sons: US Navy Captain Richard G. Thomson (adopted),[55][56][57] and Frederick Clifton Thomson[58][59][60][61] who earned a PhD in English at Yale, taught there and later joined the faculty of the University of North Carolina, later becoming an editor of the writings of George Eliot, publishing editions of Felix Holt, the Radical in 1980 and later.

In 1945, Molly, Bless Her, the 1937 novel written by Frances Marion, was adapted by Roger Burford, as the screenplay for the comedy film, Molly and Me, directed by Lewis Seiler and starring Monty Woolley, Gracie Fields, Reginald Gardiner and Roddy McDowall, released by 20th Century Fox.