Mason Fitch Cogswell was born on September 28, 1761 in Canterbury Connecticut, the third son of the Reverend James Cogswell and Alice Fitch. His mother died when he was 11 years old, and his father relocated to New Scotland Parish in Windham, CT. Mason remained behind, and was looked after by the Honorable Samuel Huntington when his father took a new wife, Martha Lathrop, that same year.

Cogswell graduated, valedictorian, from Yale College in 1780, and, at nineteen years of age, was one of the youngest of his class. Thereafter he studied medicine under his brother Dr. James Cogswell, first in Stamford, CT, as Examining Surgeon of Volunteers in the Revolutionary War, and in 1784 until 1787 in New York City. In 1789, Cogswell established himself permanently in practice in Hartford. He was active in the social life of Hartford and was intimate with the "Hartford Wits," a coterie of leading intellectual and literary figures prominent in Hartford.

In 1812 Cogswell played an important role in the founding of the American Asylum for the Deaf and Dumb (originally named the Connecticut Asylum for the Education and Instruction of Deaf and Dumb Persons). He was spurred, no doubt, by the needs of his own daughter, Alice, who was rendered deaf and mute from an illness she suffered at age two. With Mr. Gilbert, an attorney from Hebron, CT, Cogswell ascertained the number of deaf mutes in the state, and petitioned the State Legislature for funds for a school. Several years later he and six others had enough funds to allow Dr. Thomas Hopkins Gallaudet to travel to Paris and the school of Abbe Sicord to learn the necessary knowledge to establish an institute in Hartford. In 1816 he returned with Laurent Clerc one of Abbe Sicord's most respected physicians. The school was opened in 1817, with Alice Cogswell registered as its first pupil.

The school was a success, and many young physicians came to Hartford to learn from Dr. Cogswell. As Yale Medical Institution was established in 1810 Cogswell was invited to take the chair of Surgery, but as it became known that Nathan Smith, the medical educator of Dartmouth and Harvard, was available, Cogswell withdrew.

Cogswell was instrumental in establishing the State Medical Society, and served as its Secretary, Vice-President, and for ten years its President (1812-1822). He was also the first presiding officer of the Hopkins Medical Society, the precursor of the Hartford Medical Society, organized in 1846. He was awarded the honorary degree of MD by the Connecticut Medical Society in 1810, and by Yale College in 1818.

Alongside successful practice as a physician Cogswell was also an innovative surgeon, working mainly in surgical ophthalmology. He was amongst the first in the United States to operate on cataracts, and in November, 1803 he was the first American surgeon to ligate the carotid artery.

He was married to Mary Austin Ledyard, only daughter of Colonel Austin Ledyard and Sarah (Sheldon) Ledyard, of Hartford. They had four daughters and one son. Mason Fitch Cogswell died of pneumonia on December 10, 1830.