[3] The elder Cassatt was a successful stockbroker and land speculator who was descended from the French Huguenot Jacques Cossart, who came to New Amsterdam in 1662.

During his absence he devoted his time to horse breeding but still was able to organize the New York, Philadelphia and Norfolk Railroad (NYP&N), a new line that connected southern markets with the north.

New freight cutoffs avoided stations; grade crossings were eliminated; flyovers were built to streamline common paths through junctions; terminals were redesigned, and much more.

Cassatt initiated the PRR's program of electrification which led to the road being the United States' most electrified system.

However the PPR's great accomplishment under Cassatt's stewardship was the planning and construction of the long awaited tunnels under the Hudson River that brought PRR's trunk line into New York City.

In the spring of 1861, Cassatt had been hired as part of the Engineer Corps of the Pennsylvania Railroad, again as a rodman where he worked on the Connecting Railway.

[3] In 1867, Cassatt was appointed as superintendent of motive power and machinery for the Pennsylvania railroad in Altoona with a salary of $3,000 per year ($2023=65,000) when a trainman made less than $10 a week ($2023=200).

[9] Cassatt was a horse enthusiast and fox hunter who owned Chesterbrook Farm, outside Berwyn, Pennsylvania, where he bred Thoroughbred racehorses.

The 600-acre (240 ha) property is today the site of a subdivision with office buildings and homes using the Chesterbrook Farm name.

The original main barn designed by Philadelphia architect Frank Furness has been maintained and restored.

Musser, had diagnosed him with Adams-Stokes syndrome, a form of temporary hypoxia, and from early December onwards, he was attended regularly by a nurse.

[12] On the morning of December 28, a Friday, Cassatt did not feel well and decided to return to bed, though he did not complain to his wife and daughter, who were with him, of any particular pain.

[12] Despite the medical explanations for Cassatt's passing, many of his business colleagues in the railroad and financial industries immediately asserted that he had died "of a broken heart due to the sensational revelations of grafting by officials of the Pennsylvania [Railroad] system" that had come to light during recent investigations into the coal industry by the Interstate Commerce Commission.

[13]: 315 In World War II, the United States liberty ship SS A. J. Cassatt was named in his honor.