Calvin R. Hannah, obstetrician and gynecologist, the son of David and Nancy Jane (Richards) Hannah, was born on May 2, 1872, in Chrisman, Illinois. He was one of the youngest children in a large farming family. He attended Chrisman High School, De Pauw University, and the University of Illinois, and graduated on July 5, 1904, from the Illinois College of Medicine. That year Hannah went to Mexico to serve as an intern at the American Hospital; he was later assistant surgeon of the Mexican Central Railroad at Aguascalientes. In 1905 he moved to Dallas, Texas, where he set up a private practice and became assistant city health officer.
In 1907 Hannah began a long association with Baylor Hospital when he became its obstetrician in chief. The following year he became a member of the advisory board of the hospital and a professor of obstetrics at Baylor University College of Medicine (now Baylor College of Medicine). He also served as chief of staff and a member of the advisory board for Parkland Hospital from 1918 to 1920 and again from 1922 to 1935. Throughout his career he maintained a private practice, for a time in partnership with Warren E. Massey. During the decade preceding his death, Hannah's office was in the Medical Arts Building at the corner of Pacific and St. Paul streets.
He was elected president of the Dallas County Medical Society in 1914. He was the organizer and first president of the Texas Association of Obstetricians and Gynecologists in 1930 and was appointed that year by President Hoover to the White House Conference on Child Health and Protection. Hannah served as chairman in 1935–36 of the Commission on Maternal and Child Health in Texas and was a charter member and vice president in 1936–37 of the American Association of Obstetricians, Gynecologists, and Abdominal Surgeons. He was a member of the Texas Medical Association and served as its president elect in 1936–37 and as president in 1937–38. Other professional organizations to which Hannah belonged included the American Medical Association, the Dallas Southern Clinical Society, the American College of Surgeons, and the Theta Kappa Psi medical fraternity. He performed volunteer work as an instructor for the Red Cross during World War I and as president and board member of Hope Cottage. Hannah was an Episcopalian and Scottish Rite Mason and a member of the Dallas Rotary Club and Hella Temple Shrine. An avid golfer, he belonged to the Dallas Country Club and Dallas Athletic Club.
Hannah published over two dozen papers in local and national medical journals. They deal with the problems of childbirth, recommendations for prenatal and postnatal care, and the broader issues of medical ethics and education. As an obstetrician and gynecologist, he was chiefly concerned that the medical profession was focusing too heavily on surgical solutions rather than basic nutrition and prophylaxis. A colleague asserted that "his greatest usefulness in the field of gynecology was in preventing needless operations." Medicine, as Hannah saw it, was a team effort. He believed that if doctors joined to promote better education, both of the public and of medical students, the rewards would be material as well as moral. He saw socialized medicine as a threat to the profession and argued that physicians must address the broader needs of public health lest the government step in. Peer pressure, he believed, should be used to get recent medical graduates to set up practice in rural areas and to get small communities to build hospitals and share the use of expensive equipment.
On March 7, 1923, Hannah married Katherine C. Duvall. The couple was without children when, on December 16, 1940, he suffered a heart attack and died in Dallas at Baylor Hospital.