In 1847 he emigrated with his brother Daniel Harrold (1828 – 22 August 1873) on the Royal Archer, arriving in Adelaide in January 1848 and in June he took over Thomas Barnes' grocery store at 24 Hindley Street.
[4] In 1857 Joseph Harrold returned to England with his wife and two young sons, and set up a London branch of the firm in Great St. Helens, EC, very close to the Liverpool Street station, leaving the Adelaide end in the hands of his brother Daniel.
In 1873 Daniel died in 1873 and in late 1875 Joseph's sons Arthur and Ernest, born in Fullarton, South Australia but educated in England, returned to Adelaide to help run the business.
In 1882 they joined a consortium, the Adelaide Milling Company, with John Hart & Co., W. Duffield & Co., James Cowan & Co., and William Dening Glyde.
Around this time it was becoming apparent that Harrold Brothers' finances were built on a shaky foundation, but he resisted calls for him to resign from parliament.
The third brother, Leonard Frederick Harrold, the partner managing the London office, was not at first brought in as one of the creditors, then complained of having been kept in the dark about the company's insolvency, and expressed a desire to join the priesthood.