Johnston was born on January 22, 1781 at Barnboard Mill in the Parish of Balmaghie, Gallowayshire, Scotland. He was a son of John Johnston and Dorothea Johnston, who married in 1780. After his mother's death in June 1794, his father remarried to Margaret Rae in 1795, and Johnston, an only child of his parents' marriage, became the elder brother to ten half-siblings, including brothers William, Robert, Samuel, and sisters Agnes and Margaret, as well as uncle to John Taylor Sherman. His paternal grandparents were William Johnston and Janet Johnston and he was educated in the neighboring village of Laurieston, and also at Boreland.
Career
In 1804, at twenty-two years old, he came to New York and became a bookkeeper in Robert Lenox's counting house. After nine years with Lenox and Maitland, Johnston and partner James Boorman established the merchant house known as Boorman, Johnston, & Co. in 1813. The new firm, based at 57 South Street, sold Scotch goods and, later, tobacco from Virginia and wines from Madeira and Italy. They also owned an iron warehouse at 119 Greenwich Street and in 1828, admitted Adam Norrie as a partner. Johnston was elected a member of the Saint Andrew's Society of New York in 1811 and served as manager from 1819 to 1823, second vice-president from 1823 to 1827, first vice-president from 1827 to 1828 and as president from 1831 to 1832. In 1839, Johnston and several other civic-minded New Yorkers founded University of the City of New York. He was also a co-founder of Washington Square North.
Personal life
On September 2, 1817, Johnston was married to Margaret Howard, a widow of Rhesa Howard Jr.. His wife Margaret, the daughter of John Taylor and Margaret Taylor, had four siblings who, likewise, married two grandchildren, a great-granddaughter, and a nephew of Founding FatherRoger Sherman, Signer of the U.S. Constitution and the U.S. Declaration of Independence from Connecticut. Together, John and Margaret were the parents of:
John Taylor Johnston, who married Frances Colles, the daughter of Harriet Colles and James Colles, a prominent merchant in New York and New Orleans.