Samuel was born into a Jewish family in Whitechapel, London. His father, also Marcus Samuel, ran a successful import-export business, M. Samuel & Co., trading with the Far East, which Marcus carried on with his brother, Samuel Samuel. Marcus Samuel realised the potential of the oil trade during a trip to the Black Sea in 1890, and ordered the construction of eight dedicated tankers, the first of which was Murex, which was under the command of Captain John R Coundon. His were the first such ships to satisfy the Suez Canal company of their safety, allowing him to ship his product to Bangkok and Singapore. In 1897 he formed Shell, after his first business, which sold painted seashells. He was knighted in 1898 for assisting in the salvage of HMS Victorious, which had grounded and was pulled to safety by two Shell tugs.
In 1907, Samuel's company combined with the Royal Dutch company of the Netherlands to create the company today known as Royal Dutch Shell. M. Samuel & Co., having transformed over the years to a merchant bank, merged in 1965 with Philip Hill, Higginson, Erlangers Ltd to create Hill Samuel, which is now a part of Lloyds TSB.
Samuel was Lord Mayor of London in from 1902 to 1903, and received the traditional Baronetcy in 1903. In recognition of Shell's contribution to the British cause in World War I, he was created 1st Baron Bearsted of Maidstone in the County of Kent in the 1921 Birthday Honours. In 1925, he became 1st Viscount Bearsted. Lord Bearsted was also awarded an Honorary Doctorate of Law (LLD) from the University of Sheffield during his lifetime. His son, Walter Horace Samuel, succeeded him both in his titles and as Chairman of the Shell Transport and Trading Company.
His country estate at The Mote in Maidstone was sold after his death to Maidstone Borough Council for use as a public park now known as Mote Park. The house has since been used as an orphanage and a nursing home and was commandeered by the British Army during the Second World War. It is now being converted into retirement housing.