Partner, Markwith and Kline, Architects, Los Angeles, CA, c. 1948; Partner, McClellan, McDonald and Markwith, Architects, Los Angeles, CA, c. 1952; McClelland, McDonald and Markwith experimented with pre-cast concrete and tilt-up concrete buildings in the early 1950s. Partner, Buttress, McClellan, and Markwith, Incorporated, Architects, Glendale, CA, 1959-1990. This firm specialized in industrial architecture in and around Los Angeles.

B.Arch., University of Southern California, Los Angeles, CA; the 1940 US Census indicated that Markwith and his wife had both attended five years of college.

The 1920 US Census noted that nine family members, three generations, lived together in a house at 1619 North Benton Way in the Silver Lake neighborhood of Los Angeles. Markwith lived with his parents at 1607 North Benton Way in 1930. He continued to live in Los Angeles, CA, in 1935. Five years later, Markwith lived with his wife in a rented house at 1319 South Orange Boulevard in Glendale, CA. (They paid $30 per month rent at the time.) He died in the 91208 zip code of Glendale, CA, the same address as his 1990 house address, 1350 Andenes Drive.

Denver D. Markwith, Jr., came from a line of family members involved in the building industry. His grandfather, Anderson L. Markwith (born c. 1856 in OH) was a carpenter. His father, Denver D. Markwith, Sr., (born 1891 in Greenville, OH-d. 1975 in CA) worked as an electrician according to the 1920 US Census. His paternal grandmother was Frances B. Markwith (born c. 1859 in OH) and his mother was Pearl J. Rittenhouse Markwith (born c. 1890 in Hastings, NB). The 1930 US Census noted that Denver, Jr., had two brothers Charles A., (born c. 08/1908 in CA) and William G. (born c. 1920 in CA). In 1917, his parents lived at 601 18th Street in San Pedro, Los Angeles, CA, and, between 1930 and 1937, at least, at 1607 North Benton Way in Los Angeles.

He married Marjorie Markwith (born c. 1914 in PA).