Could the art dealer Algernon Moses Marsden have guessed when he commissioned the artist Jacques Tissot to paint his portrait for £50 in 1877 that nearly 150 years later the picture would warrant being saved for the nation?

Marsden was immortalised in oils at the pinnacle of his elegance and good looks. The gold signet ring and cigar he sports in the St John’s Wood studio where he sat for Tissot may have been his own, but the painter added props like a tiger skin and a Chinese vase to add a touch of exoticism and make his subject look super-debonair.

Marsden started life in 1847 as one of the 14 children of Isaac Moses, whose father Elias rose from poverty by founding a ready-to-wear clothing empire.

By 1846 their Aldgate store was the largest shop in London and within a decade Isaac had acquired a house in Kensington Palace Gardens and extended his business across the British Empire. In 1865 the family adopted their additional anglicised surname.

But, a few years after the portrait was painted, gambling debts brought to an end to Algernon’s art dealing business. Isaac helped, but eventually disinherited Algernon, although he provided legacies for his son’s wife and 10 children. Three years after Isaac’s death the son was back in the bankruptcy courts admitting to overspending in Eastbourne and at the races.

In 1901 he fled to New York with another woman and after yet another bankruptcy, died there in 1920.

Interestingly, it’s the nature of his family’s wealth that made this portrait so important in the eyes of experts.

“The painting presents precarious, recent, and specifically Jewish affluence characteristic of this era,” declared the Department for Culture, imposing an export bar in June after the portrait came up for sale by a private collector, who was asking £2.4 million for it.

Fortunately, the family’s rags-to-riches-to-rags story had reverted back to riches. Marsden’s great-grandson, Sir Martyn Arbib, and his family bought the painting as a joint acquisition for the National Gallery and National Portrait Gallery.

Now Algernon’s portrait hangs alongside artists of the day he would have admired — Cezanne, Renoir and Monet — in room 44 of the National Gallery. The painting will move to the National Portrait Gallery when it reopens next year before returning in 2024 for the National Gallery’s bicentenary.

Arbib says he was “delighted” to fund the purchase, which the family felt “very strongly” should be saved for the nation. He has an interest in common with his hapless ancestor — a love of horse-racing.

His own fortune was built on fund management, selling Perpetual Limited for more than £1billion — and the nation has reaped the benefit by way of Tissot’s portrait of a nouveau-riche Jew, an icon of the aesthetic movement.