He later manufactured cartridges for breech-loading guns, owned the Remington Arms Company and diversified into other areas of commerce.

After three years he moved to Francis Tomes & Sons, Maiden Lane, New York, and became involved with gun sales.

They purchased goods in Europe and found a ready market in New York, with Hartley specializing in guns and ammunition.

In 1857, a financial panic hit the country and many companies went under; the firm of Schuyler, Hartley and Graham survived and the following few years proved to be a boom period for them.

The company also had to defend itself in front of the grand jury when accusations were made against the partners of selling goods to the South.

[3] As war approached it became apparent that there was a major shortfall in weaponry for the armies of the North, and procurement from across the Atlantic seemed the only answer.

The Secretary of War sought advice on who could act on their behalf and the name of Marcellus Hartley was put forward.

He invested heavily in the United States Electrical Lighting Company (USELC), working with inventors such as Hiram Maxim, and using the designs of Edward Weston[6] and Moses G. Farmer.

[8] Along with Jacob H. Schiff, H. B. Claflin, Robert L. Cutting, and Joseph Seligman, he was a founder of the Continental Bank of New York in August 1870.