Growing up around the military influenced by his uncle General Stephen Watts Kearney, Philip desired the military life. However, his grandfather, who had lost his sons, preferred that Philip pursue other avenues, thus he convinced him to attend Columbia University.

So Philip went to Columbia University, and graduated in 1833, after which he traveled extensively. Upon his grandfathers death, he was bequeathed one million dollars. Philip returned home to New York, and in 1837, joined the army as a 1^st lieutenant in the 1^st U.S. Dragoons. In 1839, after serving them for two years, the U.S. secretary of war sent him to French Cavalry School at Saumur to study cavalry tactics. While in France, he saw action at Algiers, serving with the Chasseurs d'Afrique. Upon his return to the United States, he served as aide-de-camp to generals-in-chief Alexander Macomb and Winfield Scott. During the Mexican War, he remained as an aide to Scott, and at Churubusco he was wounded, so severely that it was necessary to amputate his left arm. For his heroism, Philip was breveted major general and following service in California, he resigned from the military, married and went to New Jersey to live.

In 1859 he was attracted to the military again. Serving in Napoleon III's Imperial Guard during the Italian War, he won the French Legion of Honor for bravery at Solferino. In 1861, when the Civil War began, Kearney was appointed a brigadier general of volunteers, and was placed in command of a brigade in Brigadier General William B. Franklin's New Jersey Regiment. Distinguishing himself during the Peninsula campaign, Kearney became one of the armies most respected soldiers. He was promoted to major general, and now served as commander of the 1^st Division of the III Corps, under Major General Samuel P. Heintzelman.

Following the Battle of Second Bull Run, while riding, he accidentally drifted into enemy territory during the Battle of Chantilly, and was shot and killed instantly.

His body was taken to Trinity Churchyard in New York City where he was buried on September 1, 1862. Later on his body was moved and interred in Arlington National Cemetery, Virginia. The town in which he lived in New Jersey was renamed Kearney in his honor.

In furtherance of his honor, the Kearney Medal and Cross were issued to men of the 1^st Division, III Corps for gallantry. These honors were only official insofar as Kearney's division was concerned, and not recognized by any other section of the U.S. Army.

The Kearney Medal was made of gold, in the design fashioned after the Maltese Cross, imposed with a circle containing the words Dulce et decorum est pro patria mori, and the word Kearney on a disk in the center, suspended from a ribbon. The back of the cross was engraved with the recipient's name. It was manufactured by Ball, Black & Co., of New York at a cost of about $15.00 each. Approximately three hundred seventeen were issued.

The Kearney Cross was authorized on March 13, 1863 by Brigadier General David B. Birney, who succeeded Kearney in command. Designated as the "Division Decoration," it was designed as a "cross of valor" for the enlisted men of the 1^st Division. It consisted of a bronze cross with the word's Kearney Cross on one side and Birney's Division on the other. It as well was suspended from a ribbon. Although the exact number is unknown, quite a few more of these were issued than was the Kearney Medal.

Their own regulations stipulated that no recipient of the Kearney Medal could be awarded the cross. Among the first to receive the cross were two women, Ann Etheridge and Marie Tebe.

When the Civil War began, there was no provision for awarding heroism or merit. During the war the Medal of Honor was created. Other medals for valor that came about during the war for the Union were the Fort Sumter and Fort Pickens Medals, the Butler medal for colored troops, the Gillmore Medal and the XVII Corps Medal.

In the Confederacy, the government there intended to issue medals for valor but was never able to supply them. In lieu of medals, the Confederate Congress passed an act in October 1862, providing that a Roll of Honor be published after each battle.