When observing the Comet of 1779 (discovered by Bode), Darquier discovered the Ring Nebula (M57) with a 2.5-inch, f=42 inch (110 cm) achromatic refractor (f/16.8), and according to Messier, describes it as "Nebula between Gamma and Beta Lyrae; it is very dull, but perfectly outlined; it is as large as Jupiter & resembles a planet which is fading".
He used the same telescope for observations of sunspots and other astronomical phenomena, and published a book Observations Astronomiques faites à Toulouse [Astronomical Observations made at Toulouse] (Avignon 1777) containing his observations made between 1748 and 1773.
In 1781, Darquier was among the early observers of the newly discovered planet Uranus with the same telescope, calculated an orbit for it, and found (as others) that it was a slightly excentric elliptical orbit outside that of Saturn.
Between 1791 and 1798, he created an extensive catalog of star positions, which Lalande incorporated in his catalog of nearly 50,000 stars, published 1801. Moreover, he created a French translation of Johann Lambert's "Cosmologische Briefe" (Cosmological Letters) of 1761.
Darquier died on January 18, 1802 in Toulouse at age 83.