He was born in Godalming, Surrey, the son of Sir Theophilus Oglethorpe (1650-1702) of Westbrook Place, Godalming. He entered Corpus Christi College, Oxford, in 1714, but in the same year joined the army of Prince Eugene. Through the recommendation of John Churchill, 1st Duke of Marlborough, he became aide-de-camp to the prince, and he served with distinction in the campaign against the Turks, 1716-17, more especially at the siege and capture of Belgrade. After his return to England he was elected as member of parliament for Haslemere in 1722. He campaigned for the improvement of the circumstances of poor debtors in London prisons; for the purpose of providing a refuge for persons who had become insolvent, and for oppressed Protestants on the continent, he proposed the settlement of a colony in America between Carolina and Florida. He laid the groundwork for the colonization of the state, proposing that it be colonized with debtors released from the abominable conditions of England's debtors' prisons.
Oglethorpe sailed for Charleston, South Carolina on the ship Ann, arriving in 1732, and settled near the present site of Savannah, Georgia, negotiating with the Creek tribe for land and establishing a series of defensive forts. He then returned to England and arranged to have slavery banned in Georgia.
At that time, tension between Spain and England was high, and there was a fear among the English that the Spanish colony of Florida was threatening the British Carolinas. Georgia was a key contested area, lying in between the two colonies. It was Oglethorpe's idea that British debtors should be sent to Georgia instead of imprisoned; however, no debtors were chosen to be settlers of Georgia. This, at least theoretically, would both rid England of its undesirable elements and provide her with a base from which to attack Florida. In 1739 during the War of Jenkins' Ear, fought between English Georgia and Spanish Florida as part of a larger conflict, the War of Austrian Succession, Oglethorpe was responsible for a number of successful raids on Spanish forts, as well as the unsuccessful siege of St. Augustine.
In 1745 Oglethorpe was promoted to the rank of major-general. His conduct in connection with the Jacobite Rebellion of that year resulted in his court-martial, but he was acquitted. In 1765 he was raised to the rank of general. He died at Cranham Hall, Essex.