He and his brother made their fortune in the wool trade, and in supplying fabric to the army in the period before, during and after the French Revolution.

[1] Florentin and his brother Aimé (1742–1793) expanded the family business to become suppliers of clothing and guns to the army.

[3] In 1789 the Seillières obtained the lease of the royal forge of Ruelle, which had been managed by Ignace de Wendel (1741–1795).

In 1811 François de Wendel signed two bonds of 120,000 and 180,000 from Seillière in order to buy the Moyeuvre foundry from Marin.

[6] Florentin's son Nicolas created a branch of the bank in Paris in 1798, and specialized in recovering public debts held by companies supplying the army.

[2] Florentin's other son François-Alexandre joined his brother in Paris in 1805, and in 1808 founded a bank at the Rue Le Peletier in the 9th arrondissement.