In 1869, he moved to Manchester (known as Cottonopolis in the 19th century), a major center of cotton and textile processing industries, from where he helped ship goods to his father in Tabriz.

Not only did he learn the secrets and crafts of the textile industry in Manchester, but he also delved into the intricacies of European business and English culture.

In the first floor of the hotel Caucasus, located in Erivansky Square, the Mantashevs opened a cotton store, then another one, eventually becoming fully engaged in the wholesale textile trade.

His chief accountant recalled that not a single document went into effect without Alexander's resolution, "Asttsov" ("with God" in Armenian).

Mantashev, not being afraid of high risk investments, bought (together with another Armenian colleague, Michael Aramyants) unprofitable oil wells in Baku that very soon became profitable.

In 1894 he created a tentative association along with the other major oil interests in Russia, the Nobels and the Rothschilds, in order to cooperate in the marketing of petroleum products within certain geographical areas.

[1] In 1896, during a trip to Egypt, Mantashev met Calouste Gulbenkian who was fleeing the Ottoman Empire with his family as a result of the Hamidian massacres.

(The young Joseph Stalin organized strikes in Mantashev's Batumi factory and participated in street demonstrations in 1902.

)[3] In England Mantashev bought two tankers, which supplied oil to India, China, Japan and the Mediterranean countries.

Mantashev and Co.", opening representative offices and warehouses in the major cities of Europe and Asia: Smyrna, Thessaloniki, Constantinople, Alexandria, Cairo, Port Said, Damascus, Paris, London, Bombay and Shanghai.

Surrounded by a group of geologists and petroleum engineers, he visited the sites asking countless questions, carefully studying land-color, softness etc.

Mantashev hand-picked fifty talented young Armenians and sent over two hundred to study at the best universities of Russia and Europe.

The most famous donation made by Mantashev remains the Armenian Church of St. John the Baptist in Paris on Jean Goujon street.

His body was moved to Tiflis and buried next to his wife at the cemetery of Vank Cathedral which was being restored at the time with his donations.

Today he is remembered in Tbilisi for his charity, where many of his buildings are still standing, and in Yerevan, where a downtown street was named after him along with a major luxury goods store.