Although born in a well-to-do Church of England family, at the age of 25 Penn was joined the Quakers. The Quakers obeyed their 'inner light', which they believed to come directly from God, refused to bow to the authority of the king, and endorsed pacifism. These were times of turmoil, just after Cromwell's death, and the Quakers were suspect, because of their heretic ideas and because of their refusal to pay respect to the king or swear an oath of loyalty to him (Quakers do not swear any oaths).
Penn was arrested several times, among which was a famous trial when he had been arrested together William Meade for preaching before a Quaker gathering. Penn pleaded for his right to see a copy of the charges layed against him and the laws he had supposedly broken, but the judge, the Lord Mayor of London, refused - even though this right was guaranteed by the law. Despite heavy pressure from the Lord Major to convict the men, the jury returned a verdict of 'not guilty'. The Lord Major then had not only Penn (on a charge of Contempt of court) sent to jail again, but also the full jury. The members of the jury, fighting their case from out of prison, managed to win the right for all English juries to be free from the control of judges.
The prosecution of Quakers became so fierce, that Penn decided that it would be better to try to found a new, free, Quaker settlement in North America. Some Quakers had already moved to North America, but especially the New England Puritans were as negative towards Quakers as the people back home, and some of them had been banished to the Caribbean.
In 1677, Penn's chance came, as a group of prominent Quakers, among which Penn, received the colonial province of West New Jersey (half of the current state of New Jersey). That same year, two hundred settlers arrived, and founded the town of Burlington. Penn, sho was involved in the project but himself remained in England, drafted a charter of liberties for the settlement. He guaranteed free and fair trial by jury, freedom of religion, freedom from unjust imprisonment and free elections.
King Charles II had a large loan with Penn's father, and settled it by granting Penn a large area west and south of New Jersey. Penn called the area Sylvania (Roman for woods), which Charles changed into Pennsylvania. Perhaps the king was glad to have a place where religious and political outsiders (like the Quakers, or the Whigs, who wanted more influence for the people's representatives) could have their own place, far away from England. Although Penn's authority over the colony was officially subject only to that of the king, he implemented a democratic system with full freedom of religion, fair trials, elected representatives of the people in power, and a separation of powers - again ideas that would later form the basis of the American constitution. The freedom of religion in Pennsylvania (complete freedom of religion for everybody who believed in God) brought not only English, German and Dutch Quakers to the colony, but also Huguenots (French Protestants) as well as Lutherans from catholic German states.
In 1682-1684 Penn was in Pennsylvania himself. After the building plans for Philadelphia had been completed, and Penn's political ideas had been put into a workable form, Penn explored the interior. He befriended the local Indians. He ensured that the Indians were paid fairly for their lands. He also introduced laws saying that if a European did an Indian wrong, there would be a fair trial, with an equal number of people from both groups deciding the matter. His measures in this matter proved succesful: even though later colonists did not treat the Indians as fairly as Penn and his first group of colonists had done, colonists and Indians remained in peace in Pennsylvania much longer than in the other British colonies.
Penn visited America once more, in 1699. In these years he put forward a plan to make a federation of all English colonies in America. There have been claims that he also fought slavery, but that seems unlikely, as he owned and even traded slaves himself. However, he did promote good treatment for slaves, and other Pennsylvania Quakers were among the earliest fighters against slavery.
Penn had wished to settle in Philadelphia himself, but financial problems forced him back to England in 1701. His financial advisor, Philip Ford, had cheated him out of thousands of pounds, and he had nearly lost Pennsylvania through Ford's malversations. The next decade Penn's life was mainly filled with various court cases against Ford. He tried to sell Pennsylvania back to the state, but while the deal was still being discussed, he was hit by a stroke in 1712, after which he was unable to speak or take care of himself. Penn's family would remain the official owners of the colony of Pennsylvania until the American Revolution.
original version (copied with permission)