John Mason Cook was born on January 13, 1834, in Market Harborough, Leicester, England.

He was the son of Thomas Cook (1808-1892), the founder of the Thomas Cook Travel Agency. In 1865, he was appointed head of a new office on Fleet Street, London. An energetic man, he made an immediate impact, and the subsequent growth of the business was due much to the son as the father. In 1871, he entered into full partnership with his father and the firm became known as Thomas Cook & Son, with invested capital of over £250,000. He travelled on business an average of 50,000 miles a year between 1855 and 1873. The travel agency offered railway excursions around Britain, tours of Europe and in 1866, it took tourists to America to see scenes of the recent Civil war. By the end of the decade, it was taking people to Egypt and the Holy Land. In 1878, Cook expanded the business into a lucrative foreign banking and money exchange department and helped develop travellers' cheques. He was also a Temperance President. At the time of his death, the gross value of his estate was assessed at £390,000. Cook was succeeded in business by his three sons: Frank Henry, Ernest Edward, and Thomas Albert.

In 1861, he married Emma Hodges (1834-1902). He died on March 4, 1899, in Walton on Thames, Chertsey, Surrey, England.