He was appointed by Louis XVI as royal botanist and sent to the United States in 1785 to investigate plants that could be of value in France. He traveled with his son Francois André (1770-1855) through Canada, Nova Scotia and the United States. In 1786 he established and maintained for a decade a base, in the form of a garden in Charleston, South Carolina, from which he made many expeditions to various parts of North America. He described and named many North American species during this time. He collected many plants and seeds to send back to France. At the same time he introduced many species to America from various parts of the world, including sasanqua, tea-olive, crepe myrtle, and maidenhair tree or ginkgo. His expeditions to Central Florida namely the Cape Canaveral area and Merritt Island is referenced on the Timeline Cape Canaveral. This is referenced by a letter from St. Augustine dated April 24, 1788 where he wrote and drew pictures of the big-flower paw-paw (Latin name Asimina obovata) (Annona grandiflora Bartr).
André Michaux was a diplomat, as well as a botanist, and around 1792, Thomas Jefferson asked him to undertake an expedition of westward exploration, similar to the Lewis and Clark Expedition, the Corps of Discovery, conducted by Meriwether Lewis and William Clark a decade later. At the time of the planned Michaux expedition, Lewis was an 18-year-old protege of Jefferson who asked to be included in the expedition, and was turned down by Jefferson.
Before Michaux set out, however, he came under the influence of the French Foreign Minister to America, Edmond-Charles Genet. Genet was engaging in war-like acts against English and Spanish naval interests, aggravating relations between America, England and Spain. Part of Genet’s plan included enlisting Michaux to use his influence while in the St. Louis area to arouse the sympathies of French-born settlers in the area and cause them to form militias and take up arms against the Spanish authorities. Jefferson learned of Michaux’s plans after Andre departed, but before he was able to implement any subversive actions, and Michaux got no further along on his westward expedition than the St. Louis area. He was recalled by Jefferson, and ordered expelled from the country, but in fact never left America until 1797. He may have also used the turmoil and change of government in France as an excuse to apply for amnesty, as did Genet, who remained permanently in America.
On his return to France in 1797 he was shipwrecked and lost most of his collections. In 1800 he sailed with Nicolas Baudin's expedition to Australia, but left the ship in Mauritius after quarreling with the captain. He then went to Madagascar to investigate the flora of that island, and died there of a tropical fever. His work as a botanist was chiefly done in the field, and he added largely to what was previously known of the botany of the East and of America.
He wrote two valuable works on North American plants: the Histoire des chenes de l'Amerique septentrionale (1801), with 36 plates, and the Flora Boreali-Americana (2 vols., 1803), with 51 plates.
[Although this 1803 work appeared to be the work of the father, Francois admitted some 15 years later that the work had been completed after his father's death and published posthumously by himself and another botanist.]
His son Francois published a Histoire des arbres forestiers de l'Amerique septentrionale (3 vols., 1810-1813), with 156 plates, of which an English translation appeared in 1817-1819 as The North American Sylva.