In the 1970s, Stewart Pollens apprenticed with an American harpsichord maker, [url=https://discogs.com/artist/4084871]John Challis[/url] (1907—1974), and studied luthiery at the Metropolitan Museum Of Art's Violin Craftsmanship Institute. In September 1976, Pollens began working at the Metropolitan Museum Of Art, spending the next thirty years restoring, maintaining, researching, and lecturing on the MMA's extensive collection of over 5000 historical instruments. Pollens has also worked independently with private collectors and other museums and did keyboard restoration and recording preparation for many notable musicians, such as Leonard Bernstein, Paul Badura-Skoda, John Browning, Mieczyslaw Horszowski, Byron Janis, and Igor Kipnis.

In March 1999, he stirred a controversy after challenging the authenticity of one of the most cherished [url=https://discogs.com/artist/3610124]Stradivari[/url] violins, the 1716 "Messiah" at The Ashmolean Museum in Oxford, UK, widely publicized in mainstream media, from Wall Street Journal and The Times to Le Figaro and La Stampa. Commissioned by Ashmolean to take high-resolution detailed photographs of "Le Messie," Stewart Pollens became one of the first independent experts in many decades to gain direct access to the priceless violin for close examination. He found major discrepancies in each authenticating category, presenting his findings at the American Federation of Violin Makers and in the series of Journal of the Violin Society of America articles. Pollens described glaring issues with the violin's construction, questioned the provenance (particularly as its formal owner, Jean-Baptiste Vuillaume (1798—1875), was notorious for indistinguishable Stradivarius replicas), and cited the expert opinion of dendrochronologist Dr. Peter Klein from Hamburg University, who studied the wood growth rings on photographs and concluded that the "tree used to make the instrument's top fell after Stradivari's death in 1737." The argument subsequently died away in academic polemics without a clear resolution since the [url=https://discogs.com/label/494155]University of Oxford[/url] refused to provide anyone further access to the violin for "in situ" analysis.

Stewart Pollens has written extensively on stringed and early keyboard instruments, with ten books published since 1992, mostly by Metropolitan Museum Of Art and [url=https://discogs.com/label/110999]P. Biddulph[/url] in London, including biographies of Italian maker Bartolomeo Cristofori (1655—1731), one of the earliest inventors of fortepiano's hammer action, renowned Cremonese luthier [url=https://discogs.com/artist/6058721]Giuseppe "del Gesù" Guarneri[/url] (1698—1744), and French archetier [url=https://discogs.com/artist/6078493]François Xavier Tourte[/url] (1747—1835), often recognized as the inventor of modern Pernambuco bows.