Political career
Allen's political career began in 1727 within Philadelphia's city government, and by 1730, he was elected to the Pennsylvania House. There he supported William Penn's sons and Andrew Hamilton, who had become speaker in 1729. Together, Hamilton and Allen led the Proprietary Party, which controlled the House for much of the 1730s. Allen also communicated with Proprietor Thomas Penn regarding colonial politics. In 1735, Allen was appointed mayor of Philadelphia. The following year, in 1736, he celebrated the opening of the nearly complete State House, later renamed Independence Hall, by hosting a feast for all residents and guests of the city; it was described at the time as "the most grand, the most elegant entertainment that has been made in these parts of America."
In 1739, when both Allen and Hamilton retired from the House, the opposition Quaker Party, unhappy with the Proprietors' paper money policies and the governor's support for war with Spain, regained control for the next seventeen years. Allen lost his bid for a seat in 1740, and in 1742, the Quakers accused him of inciting sailors to riot during the Philadelphia election to intimidate their voters. The riot was unsuccessful, and Allen never ran for a legislative seat in Philadelphia again.
Allen was appointed as Chief Justice of the Supreme Court of colonial Pennsylvania, serving from 1751 to 1774. He resigned due to increasing tensions resulting from his Loyalist beliefs and health concerns. He was succeeded by Benjamin Chew.
In 1768, he was elected as a member of the American Philosophical Society.