Paul devoted himself to leading the extravagant life of an young aristocrat at gambling casinos and hotels; at his homes in Paris and in the high society favoured spa town of Deauville.

The Demidov palace on the exclusive Bolshaya Morskaya Street in Saint Petersburg was rented and finally sold in 1875 to the Italian ambassador.

Things came to such a state that Aurora's four stranded nut-sized morning gift pearls were being held by a bank as a security for the company's one million-rouble debt (c. $14,400,000 in 2017 currency).

Paul's troubled life was changed by his falling in love with a lady-in-waiting from Saint Petersburg, Princess Maria Mescherskaya.

His first marriage was 1 June 1867 to Princess Maria Elimovna Meshcherskaya (Saint Petersburg, 28 February 1844 - San Donato (or Vienna, per Ferrand), 8 August 1868).

She died two days after giving birth to a son, Elim Pavlovich Demidov, 3rd Prince of San Donato, at Hietzing in the suburbs of Vienna 6 August 1868.

Paul permanently resigned from the civil service and moved on to live a great international life as Prince of San Donato.

The mother of the new spouse, Princess Elisaveta (Lise) Trubetskaya, had lived most of her life in Paris, especially after the death of her husband Prince Pjotr Nikitich Trubetskoy (1826-1880).

They had six children:[1] Deciding that San Donato was too full of memories of his first wife, Paul bought in 1873 Pratolino,[1] a large farm, from the estate of the Grand Duke of Tuscany.

They ended up selling San Donato, and it was ceded on 5 November 1881 to Gaston Mestayer, a French business magnate, with the gardens sold separately to Nemesio Papucci and Rosselli Del Turco.

A large part of the enormous Demidov collection of artworks housed in 14 rooms at San Donato were thus dispersed in several sales and memorable public auctions, even the works gathered in the "musée napoléonien" created on Elba by his uncle Anatoly Nikolaievich Demidov, 1st Prince of San Donato and the souvenirs that had mostly been ceded to Anatole by his father-in-law Jérôme Bonaparte.

Her target areas were schools, universities, libraries, hospitals, pharmacies, folk kitchens, and single mothers' work homes.

He served with the Red Cross rather than the Russian military forces during the Russo-Turkish War and in 1883 he published the pro-Jewish "The Jewish Question in Russia".

After Paul's death, his wife, Hélène Trubetskaya, took over the management of the company because all the children were minors, with the youngest only turning seven months old.