During the American Civil War, Armour capitalized on the opportunity to sell meat to the United States Army, making millions in the process.

Armour expanded into banking and speculation on the futures market for pork and wheat by 1900, his plants employed 15,000 workers; his own wealth was in the range of $50 million (~$1.51 billion in 2023).

[2] Before the journey, Armour "had received several hundred dollars from his parents," making him, for the most part, "the financier of the party," according to biographer Edward N.

[3] In California, Armour eventually started his own business, employing out-of-work miners to construct sluices, which controlled the waters that flowed through the mined rivers.

[6] Armour demonstrated his uncanny ability as a young businessman by taking advantage of changing meat prices during and after the Civil War.

According to Deborah S. Ing, author of Philip Armour's biography in the American National Biography Online, "the most important business coup of Armour's early career occurred near the end of the Civil War when he predicted heavy Confederate losses and thus the dropping of pork prices…he made contracts with buyers at $40 per barrel before prices plummeted to $18 when the war ended in a Union victory.

After individually prospering in three different regions, Philip, Herman and Joseph reconvened in 1867 to form the flagship Armour & Company in Chicago, which packed hogs exclusively for the first eight years of its existence.

[8] Armour returned to Chicago and raised funds for the stranded Exodusters, reporting, "I talked with a great many of them and was surprised at their intelligence.

In the late 1880s, he was solicited by Peter Demens to invest in his Orange Belt Railroad running across central Florida, and one of the depots was named in his honor.

[10] In 1900, while terminally ill he wintered in Southern California, probably due to his association with Demens, and his namesake son Philip Jr. came to visit, caught pneumonia and suddenly died on January 29.

His biggest concern was ensuring that every part of the animal was made useful, "thus, out of meatpacking came auxiliary industries such as glue, fertilizer, margarine, lard, [and] gelatin.

By developing these profitable manufacturing innovations and expanding the reach of his company, Armour & Co. became one of the largest meatpacking firms in America by the 1890s.

In the book Death in the Haymarket, historian James Green notes that the supplies included "a good machine gun, to be used by them in case of trouble".

[15] Over the course of his career, Armour had broken three major strikes that had directly concerned his factories, blacklisting all of the union leaders involved.

[16] "Although his workers lived and worked in squalid conditions," the PBS series American Experience reports, "Armour was known as a philanthropist".

Miles, Commanding General of the United States Army, claimed that the major meatpacking companies of Chicago—including Armour's—were sending chemically-treated meat to soldiers fighting in the Spanish–American War.

Philip D. Armour Elementary School in South Chicago, and streets of north Redondo Beach, California, are named after prominent American businessmen of the industrial revolution.