Luigi Ludovico Marchesi was born in Milan. He joined the Milan Cathedral choir in 1765 and made his operatic debut in Rome in 1773 at the Teatro delle Dame, cast as a female character, in Marcello da Capua's comic opera La contessina. For several years, Marchesi appeared either in minor roles or minor operatic centers, but he found a valuable ally in the Czech composer Josef Mysliveček after he appeared in the latter's opera Ezio and oratorio Isacco figura del redentore in Munich early in the year 1777. Marchesi's singing in both productions was considered to be extraordinary. In a letter written by Wolfgang Amadeus Mozart to his father from Munich on October 11, 1777, it is mentioned that Mysliveček bragged of his influence with the management of the Teatro San Carlo in Naples, the most prestigious venue for the performance of Italian serious opera in Europe: he apparently had the power to recommend the engagement of singers who were to be featured in productions planned for the 1778 - 79 operatic season there. Marchesi was one of the singers that Mysliveček recommended. His first appearances in Naples were as successful as those in Munich, and they permanently established him as one of the most talented vocal artists in Italy. In all, Mysliveček created five operatic roles for Marchesi before his premature death in 1781. After Marchesi's triumphs throughout Italy in the late 1770s and early 1780s, he ventured all the way to Vienna, St. Petersburg and London, where he created a tremendous sensation and was proclaimed to be the greatest singer of his time. The Earl of Mount Edgcumbe described Marchesi's impression at London as following:

Marchesi was at this time (1788) a very well - looking young man, of good figure, and graceful deportment. His acting was spirited and expressive: his vocal powers were very great, his voice of extensive compass, but a little inclined to be thick. His execution was very considerable, and he was rather too fond of displaying it; nor was his cantibile singing equal to his bravura. In recitative, and scenes of energy and passion, he was incomparable, and had he been less lavish of ornaments, which were not always appropriate, and possessed a more pure and simple taste, his performance would have been faultless: it was always striking, animated and effective. He chose for his début Sarti's beautiful opera of Giulio Sabino, in which all the songs of the principal character, and they are many and various, are of the very finest description....

He was received with ruptures applause.

In 1796 Marchesi refused to sing for Napoleon when he entered the city of Milan. For this Marchesi was honored as a national hero by the public, as reported by Vernon Lee:

The frivolous part of society chatted and danced, and adored.... the singer Marchesi whom Alfieri called upon to buckle on his helmet, and march out against the French, as the only remaining Italian who dared to resist the 'Corsian Gallis' invader, although only in the matter of song.

Marchesi's last major appearance was in Simon Mayr's Ginevra di Scozia for the inauguration of the Teatro Nuovo in Trieste (1801). He continued to appear in public for a few more years, all the way till 1806, when he retired for good and moved to his villa at Inzago, where he died on 14 December 1829. After his retirement Marchesi did not go into obscurity; once in a while, when in good health, he used to arrange a couple of private concerts; some of them were dedicated to charity, particularly for poor orphaned children.

As an artist Marchesi was certainly one of the greatest singers of his time, and he was also a composer. In London he published his own volume set of Ariette Italiane, and also a handful of solfeggi. He maintained a collaboration similar to that with Josef Mysliveček later in life with Angelo Tarchi. Perhaps his most important roles in the later part of his career were Megacle in Domenico Cimarosa's L'Olimpiade and Lovinski in Simon Mayr's La Lodoiska. Serious opera was the natural realm for his voice type, and he rarely sang comic roles after his early appearances in Rome.

In person Marchesi might have been the handsomest castrato of all time; during his London engagement in the 1790s, Maria Cosway deserted husband and children and followed the singer around Europe for several years. Also, it is said he was adored by the whole female population of Rome. At the same time, however, Marchesi became famous for his turbulent temperament and notorious stipulations. He often insisted on making his entrance on the scene descending a hill on horseback, and wearing a helmet with multicoloured plumes at least a yard high, saying "Where am I?". Otherwise, he engaged in rivalry competitions that once nearly cost him life; the fanatic supporters of the soprano Luisa Todi, his bitter rival, attempted to poison him in 1791.