Mildred T. Stahlman, a physician and scientist who was a towering figure in providing medical care for premature babies and ailing newborns, developing a treatment for an often-fatal lung condition and establishing one of the country’s first neonatal intensive care units, died June 29 at her home in Brentwood, Tenn. She was 101.

Her death was announced by Vanderbilt University Medical Center in Nashville, where Dr. Stahlman studied, taught and conducted research for decades. No cause was cited.

Dr. Stahlman, who was one of three women in her medical school class, began her research in the 1950s, investigating problems affecting premature children. Her primary focus was on hyaline membrane disease, sometimes called respiratory distress syndrome, in which alveoli — tiny air sacs in the lungs — do not properly inflate. The condition almost always resulted in death.

In 1954, Dr. Stahlman received her first grant from the National Institutes of Health and acquired a scaled-down, infant-size version of an iron lung, a ventilator often used to treat polio patients. She performed much of her early research on lung development on newborn lambs and kept a small herd of sheep in a courtyard at the Vanderbilt medical school.

With funds from another NIH grant, Dr. Stahlman bought equipment for a nursery and laboratory, then opened an intensive care unit for premature babies and newborns in 1961. It became the model for other neonatal ICUs, which are now commonplace in hospitals throughout the country.

In October 1961, the daughter of a Vanderbilt medical student was born two months premature and was severely affected by hyaline membrane disease. (Earlier that year, President John F. Kennedy’s son Patrick had died of the same ailment less than two days after his birth.)

The girl’s parents agreed to experimental treatment with Dr. Stahlman, who pulled the iron lung out of storage in the basement. She slept on a folding bed nearby as she monitored the baby girl’s efforts to breathe on her own.

“I was there for four nights,” she told a Vanderbilt interviewer in 2005. “On the fifth day, we managed to get her weaned off.”

The medical breakthrough led to further developments, including Dr. Stahlman’s research on pulmonary function, the physiology of lung cells and a treatment using surfactant, a protein that is deficient in babies with hyaline membrane disease.

“It is hard to capture in a few sentences the profound influence Millie had for so many during her lifetime,” Meg Rush, a pediatrics professor and the president of Vanderbilt’s Monroe Carell Jr. Children’s Hospital, said in a university statement. “She founded the field of neonatology, pioneering and permanently integrating the principles of science and bedside care for prematurely born babies. Her discoveries have been instrumental in shaping the field for the past 60-plus years.”

In the early 1970s, Dr. Stahlman recognized that many babies died before they could get to hospitals. She led an effort to devise a system that would provide transportation for seriously ill infants.

“During one particular time, we had three babies [in a short time] dead on arrival,” she recalled in a Vanderbilt interview. “I said that was it. We cannot tolerate them dying on the way. We considered that you couldn’t run an ICU and accept babies if you couldn’t do transport.”

She and supporters in Nashville converted a Chevy bread truck into an ambulance, outfitted with medical equipment. The system, known as Angel transport, grew to include 30 counties in Tennessee and became a prototype for hundreds of other emergency response networks.

In addition to her research, her clinical work and her leadership of the neonatal ICU, Dr. Stahlman was a professor of pediatrics and other specialties at Vanderbilt’s medical school. Barely 5 feet tall, with her hair worn in a bun, she was a formidable — even feared — presence among students and interns.

“She was terrifying,” Rush, who trained under Dr. Stahlman, said in 2022. “But it was with an eye to make you a better physician and to challenge you intellectually, building critical thinking skills.”

Mildred Thornton Stahlman was born in Nashville on July 31, 1922, the younger of two daughters. Her mother was a homemaker, and her father was the owner and publisher of the Nashville Banner newspaper. Her sister helped establish a children’s theater in the city.

Millie, as she was known, received a microscope when she was 11 years old and was determined to become a doctor. She graduated from Vanderbilt in 1943 and from the university’s medical school three years later.

She had internships and residencies in Cleveland, Boston and Chicago, and spent a year in Sweden studying cardiopulmonary physiology. After joining the Vanderbilt medical faculty in 1951, she led its neonatology unit from 1961 to 1989.

Dr. Stahlman, a past president of the American Pediatric Society, recognized that medical science alone was not enough to solve the problems associated with premature birth and infant mortality.

“We cannot afford to ignore the cumulative results of lifetimes of poor medical and social care on pregnancy outcome much longer,” she wrote in the Journal of Pediatrics in 1996. “Band-Aid medicine will no longer suffice. We must prevent what we cannot cure.”

Dr. Stahlman, who never married, often worked evenings and weekends on her research projects. She lived in a log house on a 700-acre farm in Humphreys County, Tenn., surrounded by dogs and horses. She established a college scholarship fund for students from the rural area in which she lived.

She invited her students and colleagues to her farm for holiday parties, sometimes shooting mistletoe berries out of trees with her shotgun.

She had no immediate survivors.

Through the years, Dr. Stahlman stayed in touch with many of her former students and patients — including the premature baby girl who began breathing in Dr. Stahlman’s iron-lung ventilator in 1961. Martha Lott, as she is now known, became a biomedical engineer and a mother of two before attending nursing school. For the past 20 years, she has been a nurse in the neonatal unit of Vanderbilt Children’s Hospital.