Casey was born in the Georgetown section of Wilkes Barre, Pennsylvania in 1875 – the oldest son of an Irish immigrant family.

In 1883 at the age of eight, Casey was a breaker boy in Plymouth, Pennsylvania, responsible for breaking the slag off of coal fragments as they were excavated from the mine.

According to his grandson, Terry W. Casey: "he used to speak about his excitement towards days with the occasional noontime break, which could last almost an hour in length.

In 1900 the United Mine Workers President John Mitchell visited the Pennsylvania anthracite region and Casey quickly made a name for himself as a union organizer.

During his political career Casey espoused the views of organized labor and was aggressive in educating both his colleagues and the general public about the issues pertaining to safe working conditions for miners and collective bargaining for unions.

Additionally he staunchly opposed several acts of anti-immigration legislation specifically targeting immigrants from eastern and southern Europe.

His funeral took place nine days later in his home town of Wilkes Barre, Pennsylvania, where approximately 20,000 people lined the streets to show their affection for the late congressman.

The congressman – an Irish miner at 6 feet 5 inches (1.96 m) and 250 pounds (110 kg) – was reputed to regularly split desktops in half with a strong blow.