He is best known for signing, on 23 April 1701, the "Articles of friendship and agreement between William Penn and the Susquehannah, Shawonah, and North Patomack Indians," that designated lands and conditions of coexistence between those tribes and the English settlers.
He was living with his father in Illinois in 1674 when his village was visited by Louis Jolliet and later by René-Robert Cavelier, Sieur de La Salle, accompanied by Martin Chartier.
Chartier led a mutiny against La Salle in 1680 and became an outlaw, fleeing first to upstate New York, but later returning to live with Opessa's family at Starved Rock (later known as Fort St. Louis).
[11]: 218 [7] But the provincial authorities were suspicious of Opessa's brother-in-law Martin Chartier and he was arrested, spending several months in jail in St. Mary's and Anne Arundel Counties as "a spy or party with designs of mischief," before a court determined that he was not working for the Government of New France.
[citation needed] In 1698 Opessa's band applied to the Conestoga people, and through them, to William Penn for permission to settle permanently on Pequea Creek in Lancaster County.
On 23 April 1701 Opessa and chiefs of the Susquehannock, Piscataway and Onondaga tribes signed a treaty with William Penn ceding lands along the Potomac River to the English in return for protection and trade privileges.
Opessa and the other chiefs agreed by their "hands and seals," with each other, with William Penn and his successors, and with other inhabitants of the province, "to be as one head and one heart, and to live in true friendship and amity, as one people.
According to Egle, "Opessah had taken a journey to New Castle to remonstrate with the traders who had intercepted their hunters, gave them rum, made them drink, robbed them of their skins, and when they got to [their] wigwam, they were naked and hungry.
Charles Augustus Hanna states: Deputy Governor Charles Gookin visited Conestoga with four members of his Council to investigate this murder; and while there, the Senecas gave him the following account of the affair: "That Opessa [chief of the Shawnees], being thereto solicited by John Hansson Steelman, had sent out some of his people, either to bring back or kill Francis Le Tort and his company.
[25]: 533–34 Gookin offered a clear absolution to Opessa for his role in Le Tort's death, saying: The laws of England [are] such that whosoever Kill'd a man must run the same fate; Yet considering the previous circumstances to that murder, the length of time since the action...and [that] all the persons save one (who is absconded) since [are] Dead, I am willing to forbear further prosecution on Enquiry into it, but with all caution you that if any such thing hereafter falls out, you may be assured I know well how to Do Justice as I have now shewed you mercy.
[8]: 153 In 1715 Opessa attended a conference in Philadelphia with Sassoonan,[8]: 101 [17]: 315 using the occasion to reassert the alliance between the Shawnees and the Lenape and advocating for control of rum sales to Native American communities, which were starting to undermine social cohesion due to alcohol-inspired violence and the tendency of men to make poor trade deals when intoxicated.
[27] Although he took on the role of Pekowi chief, Cakundawanna was not recognized by many members of the tribe, as Secretary James Logan reported after meeting him at Conestoga in July, 1720: "When their king, Opessah...took the government upon him, and the people differed with him, he left them.
Shawnee and Lenape communities were starting to move west into the Ohio River Valley, pushed out of Pennsylvania by the rapidly growing European population and by conflicts over land rights and alcohol, and lured by the efforts of New France to gain Native American influence with trade goods and offers of protection.
He was uncle by marriage (and father-in-law) of Peter Chartier, son of his sister Sewatha Straight Tail (1660–1759), who married his daughter Blanceneige-Wapakonee Opessa (1695-1737).