Ehrman B. Mitchell, Jr. was born in Harrisburg, PA, and graduated from the Hill School in Pottstown, PA in 1941. Mitchell entered the University of Pennsylvania in the fall of that year, but left Penn in 1943 to serve as a U. S. naval officer. After the end of World War II, he returned to Penn to earn a Bachelor of Arts and Science degree in 1947, followed by a B. Arch. with summa cum laude honors in 1948. Mitchell won the Emerson Architectural Prize and the Faculty Medal in Architecture in 1948.
Mitchell's first professional office experience was with Savery, Sheetz & Gilmour, for whom he began working in 1938. In 1951 he joined Gilboy & O'Malley, remaining with the successor firms Gilboy, Bellante & Clauss and Bellante & Clauss as an associated architect (working part of the time in London). Mitchell's future partner Romaldo Giurgola was also working as a design associate with the latter firms after 1954, when he took up long-term residency in the United States and accepted a teaching position at the University of Pennsylvania.
In 1958, Mitchell and Giurgola decided to form a partnership to pursue projects with the National Park Service. Warren Cunningham, who had also been at Gilboy & O'Malley and its successors, was also initially part of this venture, but left by 1960 to become a partner in Geddes, Brecher, Qualls & Cunningham. The work of Mitchell/Giurgola soon attracted national attention, and, in the following decades, gained international prominence. While Giurgola's role in the firm has sometimes been made more of than Mitchell's, their work has been very much a collaboration. By 1990, the founding partners retired from Mitchell/Giurgola, and their associates established the successor MGA Partners, Inc. in Philadelphia (the New York office of the firm, founded in 1966, continues with the original name).
Mitchell was a leader in the architectural profession beginning in the 1960s, and is one of a select group of Philadelphians to lead the national AIA. He first joined that organization in 1951 and was elected to fellowship in 1969. He was a director of the AIA from 1973 until 1976, vice president in 1977, first vice president in 1978, and president in 1979-1980. He has also served on the board of the Philadelphia Chapter (1964-1968), and of the Pennsylvania Society of Architects (1964-1965). He also was among the leadership of that organization in the 1960s, serving as secretary (1966), as vice president (1967), and as president (1968). In 1979, he was named an honorary fellow of the Royal Canadian Institute of Architects, and in 1980, a fellow of the Royal Australian Institute of Architects.