Ingalls was born on September 6, 1842 in Harrison, Maine, where he worked on the family farm until he began teaching at the age of 16. He attended the North Bridgton Academy and went to study at Bowdoin College. He left for Harvard Law School where he graduated from in 1863. Afterwards, Ingalls began practicing law in Gray, Maine before moving to Boston, Massachusetts, where he became an expert in corporate law, specializing in transportation lines. In 1871, he was retained as counsel to the Cincinnati and Lafayette Railroad and would eventually become its president. After multiple consolidations under his watch, the company became known as the Big Four Railroad.
