As governor, Markham helped select the site for Philadelphia, bought land from the Indians along the Delaware River and Pennsbury Manor, and began the discourse with Lord Baltimore over the disputed boundary between Pennsylvania and Maryland.
As governor of Pennsylvania, Markham contributed to the decision-making process regarding the establishment of Philadelphia, acquired land from Native American tribes near the Delaware River and Pennsbury Manor, and engaged in diplomatic efforts with Lord Baltimore over the border issue between Pennsylvania and Maryland.