James Murdock Smith was born in East Poultney, Rutland County, Vermont, on August 23, 1816, the son of merchant and Vermont legislator Harvey D. Smith and Harriet Murdock. In 1824, the family moved to Gouverneur, New York, where Smith graduated from Gouverneur Academy. He studied law in the office of Bishop & Thompson in Granville, New York, and was admitted to the bar in 1837. In 1838, he moved to Buffalo, New York, where he established a law firm with Henry W. Rogers and John J. Leonard. He began a lifelong involvement in the Episcopal Church, first at Trinity Church, and later at St. Paul's. In 1848, Smith became partners with Solomon G. Haven and formed Haven & Smith, a successful firm with ties to several prominent Buffalo financiers. In 1856, he began a stint in banking, becoming cashier of White's Bank, and a year later, Clinton Bank. From 1862-1873, he went into practice with John Ganson, after which he was appointed to a judgeship on the Superior Court in Buffalo. He retired from the bench in 1887 and died on November 27, 1899.
In 1840, Smith married Martha Bradley, who died in May 1841. Four years later, he married Margaret Sherwood, with whom he had three children: Margaret (b. ca. 1847), Harriet (ca. 1851-1855), and Philip Sherwood (b. 1863).