William Franklin's public career developed through military service, legal training, and the imperial connections of his father, Benjamin Franklin. He served with Pennsylvania troops during King George's War and later accompanied his father to Britain. After studying law at the Middle Temple, he gained appointment as royal governor of New Jersey and took office in 1763. The appointment confirmed his family's place within the imperial system.

As governor he worked with the assembly on roads, administration, and other concerns. He signed the 1766 charter for Queen's College, later Rutgers University, and sought to preserve cooperation between provincial interests and the Crown. Royal appointment, oaths, and instructions defined his authority, making colonial resistance a direct challenge to his office.

Unlike his father, William rejected the revolutionary movement. In his Two Roads address of 1775 he urged New Jersey's legislators to retain their allegiance rather than follow a course toward civil conflict. The provincial revolutionary authorities progressively displaced his government. Placed under restraint in 1776, he was imprisoned in Connecticut until an exchange in 1778. His refusal to recognize the new authorities and continued Loyalist activity made reconciliation increasingly difficult.

From British-held New York he then helped organize Loyalist resistance through the Board of Associated Loyalists. Raids and reprisals intensified the local violence of the war; the execution of the Patriot officer Joshua Huddy by Loyalists connected with the organization created a major crisis in 1782. Franklin went to Britain that year and spent the remainder of his life there, seeking recognition and support for Loyalists who had lost homes and property. He and his father had only a limited reconciliation, and their political division endured. He died in London in 1813. His career represents the imperial allegiance retained by many American colonists.