Oliver Cromwell was born on the 24/25 of April 1599. His father was Robert Cromwell and was descended from Thomas Cromwell, Earl of Essex, who was executed for treason by Henry VIII.

Oliver Cromwell was admitted into Sidney Sussex College, Cambridge.

The ancient council in Huntingdon in Cambridgeshire was abolished by a new charter and replaced by a council of twelve members elected for life and a mayor chosen out of the twelve on a yearly basis. The new system created complaints because it limited access to common land for the citizens of Huntingdon. Cromwell agreed with the complaints and became the spokesperson against the new council and its main architect Robert Bernard. The matter became serious and Cromwell was arrested and went to court. The Earl of Manchester found no-one at fault and ordered that the charter was amended to ensure the rights of people to the common land. After this episode Cromwell felt he had to leave Huntingdon. He moved to St. Ives just a few miles to the east.

Oliver Cromwell inherited land in Ely when his uncle on his mother's side, Sir Thomas Steward, died. This included farm land known as the Cathedral Tithes. Cromwell moved to Ely and lived in a house known as 'the glebe house'. This is where Cromwell and his large family lived until 1647.

With the arrival of Prince Rupert, the Parliamentarian forces led by generals Leven, Fairfax and Manchester abandoned the siege of York and headed south. Rupert followed and attacked the rear of the column forcing the fleeing army to stop. The Parliamentarians held the higher and tactically better position on Long Marston Moor. The Duke of Newcastle and his Royalist men joined Prince Rupert to create an army of around 18,000 men while the Parliamentarians had a force of around 28,000 men and had better artillery. Late in the day the fighting began with an attack by Leven and Fairfax in the centre. The attack did not go well for the Parliamentarians and Leven and Fairfax left the battlefield. Whan all seemed lost a cavalry unit commanded by Oliver Cromwell on the left of the field attacked the Royalists and gained the upper hand. The Royalists were defeated leaving some three to four thousand of their men dead.

Parliament wanted a report into the failings of the army against King Charles I. At first the Earl of Manchester was blamed for his lack of commitment in the field but, to prevent a serious split in the country, Cromwell put forward a suggestion to change how the army was controlled. Cromwell admitted that being a commander was not easy and he himself had made mistakes on the battlefield. Cromwell's suggestion was that no member of the Commons or Lords should control an army. This would mean Manchester and the other generals would have to resign. It meant Cromwell himself would have to do so as well. Cromwell suggested that the army should reorganised.

The west of England was under attack from the Royalist Western army commanded by Goring. The New Model Army was not ready and so Parliament ordered Cromwell to rejoin his regiment and to meet up with Waller. This went against the Self-Denying Ordinance under which Cromwell should have given up his command, but without his leadership Cromwell's regiment had become ill disciplined and mutinous. This was reversed when he again took command.

Sir Thomas Fairfax and the New Model Army caught the King at Naseby Field in Northamptonshire. Cromwell joined Fairfax and the combined Parliamentary force consisted of some 14,000 men while the King and Prince Rupert had around half that number. The King had a better position on the battlefield and had more experienced soldiers while some of the Parliamentary men were raw conscripts. For the Parliamentarians, Skippon commanded the infantry, Cromwell commanded the Ironsides to the left and to the right Ireton commanded his men. Both Skippon and Ireton were injured in the battle. Ireton was captured but managed to escape. Cromwell's Ironsides routed the Royalist army and the battle was won. King Charles was defeated. King Charles and his cavalry escaped to Leicester but he left has baggage train behind unprotected. Large amounts of the King's and his supporters money was captured by the Parliamentarians along with the King's personal letters.

Cromwell took his forces into Wiltshire and captured Devies, Laycock House and Winchester, after a siege, from Royalist garrisons.

The armies of Fairfax and Cromwell surrounded the city of Oxford where King Charles was besieged. Negotiations were held in an attempt to get a peaceful solution rather than lose men in a costly assault, but before the city surrendered Charles managed to escape in disguise. Charles hoped that the Scots would support his cause against Parliament. Charles had been using the French envoy, Jean de Montreuil, to communicate with the Scots.

The marriage of General Henry Ireton to Bridget, the eldest daughter of Oliver Cromwell.

Cromwell ordered that the castle at Haverfordwest should be demolished.