Trembley was born at Geneva in Switzerland. In the uprising of 1733, however, his father Jean, a leading politician and soldier, was driven from office and into exile. The fall in the family's fortune forced Trembley to seek employment. He moved to Holland in 1733 and served as tutor to the children of various noblemen. While working for Count Bentinck he read the Mémoires of René Réaumur, which so stimulated him that he began to observe nature himself. During the next few years he made a number of discoveries which were to astound Europe.

At first he worked on parthenogenesis in aphids. Though he achieved some interesting results the work was basically derivative, having already been carried out by Réaumur and Charles Bonnet. At the same time he was studying polyps or, in modern terminology, hydra, of the species Chlorohydra viridissima. They were assumed to be plants but one day in the summer of 1740 Trembley observed them to move their ‘arms’. At first he assumed that the movement was caused by currents in the water. When he swirled the jar around, expecting to see the hydra sway with the vortex, he noted that they suddenly contracted to a point, their tentacles seeming to disappear in the process. As the water calmed, the polyps stretched and once more revealed their tentacles. He was still unsure, however, whether they were plants or animals. There was, he realized, a simple procedure he could carry out to resolve the dilemma. If they were animals, then they would surely die if cut into two; plants would continue to grow.

In late 1740 he divided a number of polyps transversely. To his surprise he found that within a few days the two parts had not merely grown, but had developed into two perfect polyps: the tail grew a head, and the head a tail. He published his results in his Mémoires…à l'histoire d'un genre de polypes d'eau douce (1744; Memoirs on the Natural History of Freshwater Polyps). Polyp samples were also dispatched to scholars and institutions throughout Europe. Some, particularly vitalists, found Trembley's work difficult to accept. What happened to the animal's soul? Was that also divided into two? Others saw it as evidence for the oneness of nature, the ‘Great Chain of Being’, with the polyp being the link between plants and animals. Embryologists saw in the polyp conclusive proof against the preformationists who claimed that embryos were minute but preformed individuals. These and other issues were endlessly debated throughout the century, and Trembley's polyps became the best-known invertebrates in Europe.

Trembley himself had little more to contribute to science. He left his post with Bentinck in 1747. Thereafter he traveled around Europe, engaged in some kind of diplomatic activity for Britain, for which he received a pension of £300 per annum for life, and wrote a number of books on education, politics, and philosophy.