[2] On August 22, 1843, following a long and frustrating courtship, he married Sarah Jane Negley, daughter of Jacob and Barbara and aunt of James S.

In 1859, he was elected assistant judge of the Allegheny County Court of Common Pleas and on December 1 began a ten-year judicial career.

Mellon invested the proceeds from his legal work shrewdly, buying up large portions of downtown Pittsburgh real estate.

In late 1869, he decided to retire from the bench, and rather than return to the legal profession, "concluded to open a banking house.

[5] Above the cast iron door of the original bank building at 145 Smithfield Street was placed a near life-sized statue of his inspiration, Benjamin Franklin.

Shrewd investments included real estate holdings in downtown Pittsburgh, coal fields, and a $10,000 loan to Henry Clay Frick in 1871, which would provide the coke for Andrew Carnegie's steel mills.

Though not devoutly religious,[9] he was a member and supporter of the East Liberty Presbyterian Church, the land for which had been originally contributed by the Negley family.

He maintained a "country house" at 401 North Negley Avenue in East Liberty, where he indulged a passion for horticulture, raising fruit trees and other crops.