He enlisted in the military in Bethlehem, PA, at the age of 16 (serving from October 1755 through February 1756) in Isaac Wayne's company that was part of the Pennsylvania militia during the French and Indian War.

However, Franklin decided against filling that role and was succeeded by Col. William Clapham who participated in the construction of several forts in Pennsylvania during the war.

Miles became a lieutenant at age 19 and was put in charge of the small garrison in Shippensburg, a settlement that straddled Cumberland and Franklin counties.

Miles, an early advocate for American independence from England, quickly entered politics, and was elected to Pennsylvania's House of Assembly in 1772.

As a senior member of Washington's command staff, Miles took part in that battle that took place on the western end of Long Island in present-day Brooklyn.

When the tide of battle turned against the Americans, Miles commanded a holding action that allowed Washington and the bulk of his outnumbered troops to escape.

[8] Joining with financier Robert Morris, he helped underwrite the voyage of the ship Empress of China – the first American vessel to visit the Chinese mainland.

Miles started the ironworks at Centre Furnace in State College in 1791 as a joint venture with James Dunlap and John Patton.

He also built the ironworks at Harmony Forge and the town of Milesburg soon grew, populated by the iron workers drawn to the ore-rich land on the banks of Spring and Bald Eagle creeks.

They became the parents of 10 children, three of whom died in childhood: Hannah (1764-1845), Samuel (1767-1767), Abigail (1768-1823), James (1770-1797), Catherine (1771-1771), Sarah (1772-1775), Mary (1775-1835), John W. (1778-1829), Joseph (1780–1841), and Charles (1783-1814).

[11][12] Miles's portrait, painted by the noted American artist Gilbert Stuart, hangs in the National Gallery of Art in Washington, DC.

Miles died at the age of 66 on December 29, 1805, in Whitemarsh Township, Pennsylvania, and was interred at Mount Moriah Cemetery in Philadelphia.