He had a long family history of physicians and surgeons, starting with his grandfather Benjamin Welch.

[3] William H. Welch was educated at Norfolk Academy and the Winchester Institute, a boarding school.

Initially, Welch was not interested in becoming a physician; his primary ambition was to teach the Greek language.

After a short period of teaching high-school students in Norwich, New York, Welch went to study medicine at the Columbia University College of Physicians and Surgeons, in Manhattan.

Medical schools and institutes across the country vied for Welch's former students and graduate scientists to fill top posts.

[1] Many of his residents went on to become highly prominent physicians, including Walter Reed, co-discoverer of the cause of yellow fever, Simon Flexner, founding director of the Rockefeller Institute for Medical Research, and future Nobel laureates George Whipple and Peyton Rous.

He was an instrumental reformer of medical education in the United States, as well as a president of the National Academy of Sciences from 1913–1917.

Welch served in the U.S. Army Medical Corps during World War I, and played a major role in the response to the 1918 Influenza Pandemic.

[9] Welch died on April 30, 1934, at the age of 84, of prostatic adenocarcinoma at Johns Hopkins Hospital.