O'Meara spent his childhood in Cloquet, Minnesota, graduating from Cloquet High School in 1914. O’Meara started his college education at the University of Minnesota before taking a leave of absence to serve in the US Army in World War I. Upon his return, he completed his studies in journalism at the University of Wisconsin–Madison, graduating Phi Beta Kappa in 1920.
O’Meara stayed on in Minnesota for several years, writing for the Duluth News Tribune. Following his time with the newspaper, he moved to Chicago to work for the advertising agency J. Walter Thompson. In 1932 he relocated to New York to work for the advertising agency Benton & Bowles, but in 1942 rejoined J. Walter Thompson, at their New York office.
O’Meara went on to act as the Chief of Planning for the Office of Strategic Services, as well as the head of the information department of the Office of Price Administration, during World War II. In 1950, following World War II, O’Meara decided to pursue a career in writing. Over the span of his career, he saw a number of magazine article published, in addition to 16 books. Two of these books, Minnesota Gothic and Grand Portage, were best-sellers.
O’Meara was married in 1922 to Esther Arnold, with whom he had four children: Donn, Ellen, Deirdre,and Wolfe. They lived in several places including Washington Mews, NYC; Woodstock, NY; and Danbury, CT. He died in Massachusetts in 1989, at the age of 92. 
O'Meara is the author of a number of publications:
- Trees Went Forth 1947
- Grand Portage 1951
- Tales of the Two Borders 1952
- Spanish Bride 1954
- Minnesota Gothic 1956
- Devil's Cross 1957
- First Northwest Passage (Illustrated by Lorence Bjorklund) 1960
- Savage Country (Illustrated by Philip B. Parsons) 1960
- Last Portage (llustrated by William Hofmann) 1962
- Guns at the Forks 1965
- Duke of War 1966
- Daughters of the Country; The Women of the Fur Traders and Mountain Men 1968
- Sioux are Coming (Illustrated by Lorence Bjorklund) 1971
- We Made It Through the Winter: A Memoir of Northern Minnesota Boyhood 1974
- Guns at the Forks 1979
- Minnesota Historical Society. "WALTER O'MEARA: An Inventory of His Papers at the Minnesota Historical Society." Accessed June 28, 2007.
- "http://query.nytimes.com/gst/fullpage.html?res=950DE1D61439F931A35753C1A96F948260 New York Times obituary"
- Library of Congress Online Catalog. "WALTER O'MEARA" Accessed June 28, 2007.