The driving force behind the bank, and its first chairman, was Halifax businessman and former mayor, William Machin Stairs (1789–1865).

In the nine years he was in charge, William Machin Stairs began an expansion of the bank that his successors continued.

The Union Bank's executive at the time failed to recognize the need for expansion into the growing national market.

Within a few years, increased competition from much larger financial institutions meant a merger with another bank was essential for survival.

The noted financier Izaak Walton Killam began his business career in his hometown of Yarmouth, Nova Scotia as a junior clerk at the local branch of the Union Bank of Halifax.