Born in Marolles-les-Braults in the French department of Sarthe, Coutard attended medical school at University of Paris and graduated in 1902.

He served in the French Army and lived for several years in the Jura Mountains before returning to Paris to study the medical applications of radium.

He became the chief of the X-ray department at the Radium Institute of the University of Paris in 1919, working closely with Claudius Regaud and other scientists.

[3][4] His research centred on therapeutic applications of radium in animals, and he presented his work at the 1912 meeting of the French Association for the Advancement of Science [fr].

[3] Coutard was drafted during World War I and worked as a radiation therapist in a military hospital near Baccarat, Meurthe-et-Moselle, on the Eastern Front.

[6][9] In 1919, Coutard became the chief of the X-ray department at the Radium Institute of the University of Paris, working with other scientists including Regaud and Antoine Lacassagne.

[4][9] Using a single X-ray unit in the basement of the institute, he conducted experiments on animals, administered radiation therapy to patients, and performed diagnostic imaging of the pharynx and larynx.

[11] At the 1921 International Congress of Oto-Rhino-Laryngology in Paris, Coutard presented data from six patients with laryngeal cancer who he had treated with radiation.

[12] Coutard believed that long durations of radiation, applied over several weeks, produced the best results and theorised that this technique allowed tissue to recover between sessions.

[15][16] Though he never published rigid standards for radiation doses, he meticulously recorded the treatments that he administered to each patient, using a radiometer that he constructed.

[10] Radiotherapists from other countries visited the Radium Institute to meet Coutard and train with him,[9] including Simeon T. Cantril, who later became the first president of the American Society for Radiation Oncology.

[20] The physicist Charles Christian Lauritsen, on behalf of his mentor Robert Andrews Millikan, invited Coutard to work at the Kellogg Research Laboratory at the California Institute of Technology.

He began to conduct unorthodox experiments, including the use of blocks of gold as X-ray filters and homeopathic theories of beta particles, and stopped publishing papers in scientific journals.

[25] According to the radiologist and historian E. R. N. Grigg, the monograph was a "rambling mixture of clinical observations, working hypotheses, and fantastic assumptions"; it was largely ignored by reputable journals as well as his peers.

[28] While Coutard's experiments in final years were considered unorthodox by his peers, his earlier contributions helped radiation therapy become an established treatment for people with cancer.

Grigg described Coutard's most important contribution as "teaching a generation of radiologists to observe their patients carefully and to record painstakingly the clinical course of treatment".