He introduced the use of the term facies in geology, and is considered one of the founders of modern stratigraphy and paleoecology.

He initially studied medicine at Strasbourg, but his interest subsequently switched to geology, and from 1836 onward, he worked as an assistant to Louis Agassiz.

In 1838 he published Observations géologiques sur le Jura Soleurois (Geological observations involving the Solothurn Jura), in which he introduced the "concept of facies" to describe the environments and conditions of the origin of sedimentary rocks based on their petrographic attributes and fossil affiliations.

[1] In 1859 he was sent by Eduard Desor to Cette on the Gulf of Lyon in order to investigate the mode of life of marine organisms,[3] and in 1861, with Carl Vogt and others, he embarked on a scientific expedition that took him to the North Cape, Jan Mayen and Iceland.

Near the end of his life, Gressly suffered a mental decline and was committed to an asylum near Bern.