Mecklem was born in Colfax, Washington on December 17, 1890. (He later often gave his birth year as 1894, but the earlier date has been confirmed by a family record and by a signed, witnessed 1926 application by Mecklem to the Navy for adjustment to compensation for his naval reserve service.) Mecklem was a son of Archibald McDanel Mecklem and Laura Isobelle Smith. One of Austin's brothers was Llewellyn Guy "L. G." Mecklem (1882-1973), daredevil aerialist and racecar driver, who made the first powered flight over Seattle, in a hydrogen-filled airship, in 1908.[5]
Mecklem married Hannah Small about 1923. The couple lived in the Maverick "art colony" in Woodstock, New York, then moved to Portland, Oregon, where Mecklem taught painting and had his first solo show, at the Portland Art Museum in 1928. Austin and Hannah traveled to Europe in 1929, and resided in New York City for a time. Hannah Small became romantically involved with the painter Eugene Ludins, and eventually Small and Mecklem divorced, after which Small married Ludins.
Mecklem married Marianne Appel in 1937.[3] They lived at the Maverick colony in Woodstock in a cabin. Mecklem died on October 7, 1951.[7] Austin and Marianne had two children, Sarah Greer Mecklem and Margaret Merrill Mecklem. After Austin's death, Marianne moved, with her daughters, to New York City, where she worked as a puppet designer, and authored and illustrated children's books; she later worked for Jim Henson. In 1960, she married Carl Harms, an actor, puppeteer, and board member of Actors Equity.