Peter Sides was born in 1820 in Philadelphia, Pennsylvania. He was a merchant there before the war.

On September 4, 1861 he became Captain of Company A of the 57th Pennsylvania Volunteer Infantry Regiment when it was organized at Harrisburg, Pennsylvania. The regiment became part of the Third Corps of the Army of the Potomac. It took part in the Peninsula Campaign from March until August of 1862, and in the Second Bull Run Camaign in August of 1862.

On September 15th, 1862, Sides was promoted to lieutenant colonel. The 57th Pennsylvania and the Third Corps were not involved in the Battle of Antietam, remaining near Washington D.C.

Sides took command of the regiment in December when Colonel Charles T. Campbell was promoted to brigadier general. The regiment was in reserve at the Battle of Fredericksburg in December of 1862.

On March 12, 1863, Sides was promoted to colonel. He commanded the 57th Pennsylvania at the Battle of Gettysburg on July 1-2, 1863, when it lost 115 casuaties out of the 207 men engaged. The regiment fought north of the Peach Orchard on July 2, where its monument is today. Sides was wounded in the left hand.

He returned to command the regiment until May 5, 1864 at the Battle of the Wilderness.  Here he was wounded again, this time more seriously in the left arm. He did not return to command, and would be discharged for disability on November 28, 1864 due to his wound.

Peter Sides returned to Philadelphia after leaving the army. He died on October 23, 1878, and is buried in Lawnview Cemetery in Rockledge.