Lvov's architecture represented the second, "strict" generation of neoclassicism stylistically close to Giacomo Quarenghi. Lvov worked in Saint Petersburg but his best works survived in the countryside, especially his native Tver Governorate. He redesigned the external appearance of Peter and Paul Fortress and created an unprecedented Trinity Church combining a Roman rotunda with one-of-a-kind pyramidal bell tower. He adapted rammed earth technology to the environment of Northern Russia and used it in his extant Priory Palace in Gatchina; Lvov's construction school, established in 1797, trained over 800 craftsmen. He managed geological surveys and published a treatise on the coals from Donets Basin and Moscow Basin. He experimented with coal pyrolysis, proposed new uses for coal tar and sulphur, and wrote a reference book on heating and ventilation.
Back in Saint Petersburg Lvov created a private theatre based in the Bakunin house and played lead parts in plays by Jean-Francois Regnard, Antonio Sacchini and, probably, Yakov Knyazhnin. He led otherwise a modest lifestyle of a salaried clerk, living at his friends' houses, and could not afford renting his own until May 1779 when his pay was raised to 700 roubles per annum.
Contrary to neoclassical mainstream of his age, Lvov as a poet belonged to emerging sentimentalism and pioneered exploration of "spontaneous, great-hearted sincerity in the Russian peasant" that defined yet unexplored national character. He belonged to a close-knit ring of fellow poets; its key members, Lvov, Derzhavin and Vasily Kapnist, were bonded by their marriages to three Dyakova sisters. Kapnist married Alexandra Dyakova in 1781; Derzhavin married Yekaterina Dyakova in 1795, his second marriage. Lvov, Kapnist and Ivan Khemnitser shaped poetic self-determination of their elder and better known friend Derzhavin whose literary career started in 1779. The group also included painters (Dmitry Levitzky, Vladimir Borovikovsky), musicians (Yevstigney Fomin and probably Dmitry Bortniansky), engravers and publishers; Marina Ritsarev called the Lvov ring "another Russian Academy, albeit an informal one".
Politically, Lvov was an "active royalist" faithful to Catherine and later Paul I, at the same time he was also loyal to his fraternity; he secured a diplomatic appointment to Khemnitzer, and tried to prevent the 1790 trial of Alexander Radishchev. Lvov as a mature man parted with his affection to Western culture and became "sort of a slavophile avant la lettre." He was the first to discover poetic qualities of Russian winter, previously overlooked or denied, and to turn it into a stylistic device. For him, winter became a manly nationalistic symbol of what makes Russians different from their Western and Southern neighbors. In the end, Lvov produced "perhaps the most articulate early image of the exuberant Russian soul, and the most explicitly contemptuous of the West" predating nationalist writing by Nikolai Gogol.
A list of Lvov's architectural works compiled by Tatarinov contains 87 buildings and country estates, some unconditionally attested through archive evidence, others attributed with different degree of confidence. The first work on this list, interiors of the house for Sophie Dorothea of Wurttemberg, the bride of Paul I, was commissioned by Catherine II in the summer of 1776. However, absolute majority of Lvov's works were built for private clients: Bezborodko, Derzhavin, Olenin (Utkina Dacha), Kochubey, the Vorontsov and Vyazemsky families in the 1780s.
In the same period Lvov designed the cathedral of Borisoglebsky Monastery in Torzhok, a purely Neoclassical five-domed edifice that also contained hints of Russo-Byzantine architecture, a style that emerged decades after Lvov's death. Bell tower of the same monastery became Lvov's last known design; it was started after his death by Fyodor Ananyin and completed in 1811.
The first task assigned to Menelaws was something different: searching for coal deposits in Lvov's native Tver Governorate. Lvov was concerned about Russia's dependence on imported British coals and deforestation caused by charcoal extraction, and gained support of Bezborodko and Vorontsov to survey for fossil coals. In August 1786 Lvov and Menelaws announced the find of commercial quality coal "not inferior to that from Newcastle" in Borovichi. Menelaws concurrently managed Lvov's construction projects in Torzhok and other places, raising suspicion that coal survey was merely an excuse for appropriating the Scotsman. Prospecting for coal continued for years, commercial coal mining in Borovichi commenced only eleven years later, after Paul I granted Lvov state support in his business.
The death of Lvov's benefactor Alexander Bezborodko in April 1799 slowed down Lvov's projects; Lvov himself fell ill in September 1800 and barely recovered by April 1801. In July 1801 Lvov wrote that he "returned from the other world on crutches" but managed to get through to the new emperor Alexander I and presented his album on rammed earth construction. The meeting paid back in October 1892, when Alexander granted Lvov the rank of privy councilor and appointed him to the Expedition of State Household. Lvov's health deteriorated again and he left Saint Petersburg for the Caucasus. On his way south he designed and built the foundations for the Stone of Tmutarakan in Taman and wrote a description of mineral springs of Mount Beshtau district. Spa treatment did not help, and he died on the way back, in Moscow. He was buried in a rotunda mausoleum in his native Cherenchitsy that he designed in 1784 and built in the 1790s.
Lvov's cousin Fyodor Petrovich Lvov (1766–1836), a composer, headed the Imperial Capella in Saint Petersburg. Fyodor's son Aleksey Fyodorovich Lvov (1799–1870) followed in his father's step and inherited his chair at the Imperial Chapel, but is better known as the author of the imperial Russian national anthem God Save The Tsar! (Bozhe, tsarya khrani). Hector Berlioz called Aleksey Lvov "an eminent musician, who is both virtuoso and composer. His talent as a violinist is remarkable, and his latest work, Ondine, contains beauties of the highest order..." Aleksey Lvov also ventured into ethnography, focusing on the historical liturgical singing, and even attempted to enforce, in vain, his vision of historical truth in church music.