Mohr was born on June 16, 1929, in Loup City, Nebraska, United States.
After three years with United Press in Chicago, he joined Time magazine in 1954.
His assignments for Time magazine included coverage of San Francisco, the White House, New Delhi, Hong Kong and Saigon.
During the Vietnam War, Mohr's reports appraised the policies underlying the war: attempts at secret bombing, strategic and planning failures, the use of napalm on civilians, efforts to pacify the Vietnamese people, and corruption in South Vietnam's leadership.
He suffered a fatal heart attack at his home in Chevy Chase, Maryland and died in Suburban Hospital on his 60th birthday.