Cassel was born in Cologne, in what is now Germany, the son of Amalia and Jacob Cassel. His family were Ashkenazi Jews. His father owned a small bank, but the son Ernest arrived penniless in Liverpool, England in 1869. There he found employment with a firm of grain merchants. With an enormous capacity for hard work and a natural business sense, Cassel was soon in Paris working for a bank. Being of Prussian origin, the Franco-Prussian War forced him to move to a position in a London bank. He prospered and was soon putting together his own financial deals. His areas of interest were in mining, infrastructure and heavy industry. Turkey was an early area of business ventures, but he soon had large interests in Sweden, the United States, South America, South Africa, and Egypt. One of the wealthiest men of his day, Cassel was a good friend of King Edward VII, prime minister H. H. Asquith and Winston Churchill. In 1878, he married Annette Mary Maud Maxwell at Westminster. Their only child, Amalia Mary Maud Cassel, married Wilfrid Ashley, 1st Baron Mount Temple. Cassel became a Roman Catholic at the behest of his wife, but many still considered him a Jew. The establishment was surprised to find out that he had converted when he chose to be sworn into the Privy Council with the Douay–Rheims Bible.
Retirement
Cassel retired from business in 1910. His philanthropic benefactions included £500,000 for educational purposes, £225,000 for a hospital for nervous diseases, £50,000 to King Edward's Hospital Fund in memory of his only child. He built and endowed an Anglo-German Institute in 1911 in memory of King Edward VII. He owned a castle in Switzerland, Riederfurka, which could only be safely accessed on a mule. When the inhabitants of the town nearby said they were going to make a better road to his property, he answered: "If you do, I'm not coming here anymore." Economist Felix Somary, who tells this anecdote in his autobiography, visited him there in 1914 to persuade him that war was inevitable. During World War I, Cassel made large financial gifts to the British Red Cross and other war time charitable entities working to ameliorate privation being suffered by British military casualties. Cassel had a famous art collection and many beautiful houses. He bred racehorses and owned Moulton Paddocks in Newmarket.
Family
After the early death of his wife Annette in 1881, he and his widowed sister Wilhelmina helped each other bring up his daughter, Maude, and Wilhelmina's son and daughter. Maude died as a young woman, leaving him two granddaughters Mary and Edwina on whom he doted. He was particularly attached to Edwina, who looked after him in his old age. She later married Lord Louis Mountbatten. Cassel's nephew was the barristerSir Felix Cassel, who later became Judge Advocate-General to the Forces.
In 1919, Cassel founded and endowed the Cassel Hospital, originally at Swaylands near Penshurst, and now at No. 1 Ham Common, Ham, near Richmond, London. The hospital is a therapeutic community for the mentally ill, providing residential, day and outreach services, part of the NHS.
Death
Cassel died at Brook House, Park Lane, London. His body was buried in Kensal Green Cemetery in front of All Souls' Chapel. A few months after his death, Cassel's estate was probated at £6,000,000..
