Thomas McKean (/mɪkˈkeɪn/; March 19, 1734 – June 24, 1817) was an American lawyer, politician, and Founding Father. During the American Revolution he was a Delaware delegate to the Continental Congress in Philadelphia, where he signed the Continental Association, the Declaration of Independence, and the Articles of Confederation. He served as President of Congress for four months in 1781. McKean was at various times a member of the Federalist and the Democratic-Republican parties and served as president of Delaware, chief justice of Pennsylvania, and the second governor of Pennsylvania. He also held numerous other public offices.

McKean was born on March 19, 1734, in New London Township in the Province of Pennsylvania to William McKean and Letitia Finney. His father, William, immigrated from Ireland to the colony of Pennsylvania in 1720, and was later listed as a tavern keeper.

When his mother, Letitia, died in the fall of 1742, it took a strain on Thomas's, father, William. He quickly became an alcoholic, and because of that, was incapable of raising his family. Thomas's younger sister, went to go live with their aunt and uncle, while eight-year-old Thomas, and ten-year-old, Robert began their education under Reverend Francis Alison at his school in New Castle, Delaware

During his education, McKean took on a boyhood attitude, beyond his studies. By the time he reached his adolescence, he had learned how to ride a horse and shoot a gun. Though the school was simply for boys, McKean did interact with some females, which included Reverend Alison's wife, Hannah Armitage, and her toddler half-sister, Sarah Armitage, though McKean gave her little attention, preferring to be with his friends, Charles Thomson and George Read. After a decade studying at Dr. Alison's academy, McKean's brother, Robert, left for London to study medicine This was the first time the two were separated.

In the year 1750, McKean finally finished his studies with Dr. Alison, and shortly thereafter moved in with his uncle, John Finney, who was a wealthy lawyer at the time. During this, McKean studied with his cousin, David Finney, and after four years, in 1754, he was finally admitted to the Bar (law).

At some point, McKean met Mary Borden, the daughter of Colonel Joseph Borden of New Jersey. They would marry on July 21, 1763 in Mary's hometown of Bordentown. Together, they had six children, two boys, and four girls, one of whom died in childhood. Mary Borden would die on March 12, 1773, in Delaware of an unknown cause.

Shortly after the death of Mary Borden, at some point, McKean reconnected with Sarah Armitage, who he'd marry on September 16, 1774, and would live at the northeast corner of Third and Pine streets in Philadelphia. Together they would have four children, one of whom married the Spanish diplomat, Carlos Martínez de Irujo, who was appointed to his position in 1796.

In 1755, he was admitted to the bar of the Lower Counties, as Delaware was then known, and likewise in the Province of Pennsylvania the following year. In 1756, he was appointed deputy attorney general for Sussex County. From the 1762–1763 session to the 1775–1776 session, he was a member of the General Assembly of the Lower Counties, serving as its speaker in 1772–1773. From July 1765, he also served as a judge of the Court of Common Pleas and began service as the customs collector at New Castle in 1771. In November 1765, his Court of Common Pleas became the first such court in the colonies to establish a rule for all the proceedings of the court to be recorded on unstamped paper. In 1768, McKean was elected to the revived American Philosophical Society.