Oliver Cromwell was born in a small English country estate called Huntingdon in East Anglia on April twenty-five, 1599. Of his origins, Cromwell himself wrote, "I was by birth a gentleman, living neither in any considerable height, nor yet in obscurity." Oliver's father was Robert Cromwell, a gentleman and the younger son of Sir Henry Cromwell, the "Golden Knight of Hinchbroke." Sir Henry Cromwell was himself the grandnephew of the famous Thomas Cromwell, the chief architect of King Henry VIII's political and religious reformation. Cromwell's mother was Elizabeth Steward, whose family had acquired lands confiscated by Henry VIII from the Roman Catholic Church during the sixteenth century.

Very few details are known about Cromwell's early years. Biographer Barry Coward writes that all we have are a "tiny handful of disconnected 'facts'–the equivalent of the archaeologist's pieces of broken pottery." Together with such "facts" are many myths about Cromwell's upbringing that were probably invented by Cromwell's royalist opponents after his death in 1658. One of the more amusing of these myths holds that when King James I visited the estate of Oliver's rich uncle in 1603, the four-year-old Oliver Cromwell bloodied the nose of the toddler who would later become King Charles I. One of the better- established circumstances of Cromwell's upbringing is that his mother Elizabeth had great influence on her young son. In addition to this strong female influence in Cromwell's life, the young Cromwell also had seven sisters.

Cromwell grew to be an athletic, boisterous boy who enjoyed playing practical jokes. He received his boyhood education from a Puritan minister by the name of Thomas Beard. Dr. Beard was rector of the local parish, as well as the headmaster of the local school and the author of several plays and theological tracts. One of those treatises, which Cromwell very likely read, was called The Theatre of God's Judgments. Later, in 1625, Beard wrote a tract that attempted to prove that the Catholic pope was the antichrist. It is unknown, however, exactly how much of Beard's Puritan beliefs were passed on to the young Cromwell. Some historians tend to doubt that Cromwell developed any deep religious fervor at this stage of his life. On the other hand, he was taught from an early age to detest Roman Catholicism as a corrupt, superstitious, and politically dangerous form of Christianity.

In 1616, the seventeen-year-old Oliver Cromwell packed his bags to attend Sidney Sussex College at the University of Cambridge. The faculty of Sidney Sussex was notable for being the Puritan stronghold among the Cambridge schools; its Master from 1610 to 1643, Samuel Ward, was a well-known Calvinist, one of the strictest Protestant sects. While at school Oliver seems to have excelled at mathematics, though early biographers report that he was more serious about athletics than his schoolwork.

Cromwell's education was cut short by his father's death in June 1617. As Robert Cromwell's only son, Oliver Cromwell became the legal heir and master of Huntingdon. It is unknown if he ever returned to Cambridge, although it is certain that he never took a degree there. It is also possible that during the three years following his father's death, Oliver studied law for a time at the Inns of Court in London. He may also have gone abroad to fight in the Thirty Years' War, a religious conflict that ravaged much of Europe from 1618 to 1648. However, no definite traces of his whereabouts during these years exists.

Cromwell's whereabouts come to light once again with the record of his marriage to a certain Elizabeth Bourchier on August twenty-two, 1620. The wedding took place at St Giles's Church in Cripplegate. Elizabeth was the daughter of a wealthy, knighted London merchant who was in the fur and leather trade, and her family connections were beneficial to the twenty-one-year-old Cromwell. Elizabeth's cousins, the Barringtons, were a powerful family in the English political scene. Cromwell biographer Christopher Hill writes that Cromwell's marriage "brought him closer to the heart of the powerful group which was to lead the Parliamentary opposition" to King Charles I and the Royalists during the English Civil War. For the moment, however, Cromwell settled in with his bride at Huntingdon and began raising a family. He and Elizabeth would have eight children between the years 1621 and 1638.