Appointed Governor of the Province of New Jersey in 1747, Belcher arrived when the College of New Jersey's original 1746 charter was under attack by unsympathetic Anglicans. Belcher, a Congregationalist, had been alienated by religious developments at his alma mater, Harvard, and sympathized with the fledgling college in New Jersey. On September 14, 1748, Belcher granted a second charter, which expanded the trustees from 12 to 23, stipulating that the governor would chair the Board of Trustees and that four seats would be reserved for members of the New Jersey Council. He also added three leading Philadelphians, placating a group that had felt excluded. These appointments, by not specifying religious affiliation, made Princeton the first American college whose trustees were drawn from more than one denomination.
On November 9, 1748, at the College's first Commencement, the trustees conferred on Belcher Princeton's first honorary degree.
Belcher encouraged the trustees to raise funds for a college building and played a central role in its location. While Newark, Elizabeth and New Brunswick were initial favorites, Belcher threw his influence behind Princeton — "as near the center of the Province as any and a fine situation."
Just before the College moved to Princeton, Belcher donated his 474-volume library, a full-length portrait of himself, his carved and gilded coat-of-arms, a pair of terrestrial globes, and portraits of 10 kings and queens of England. In gratitude, the trustees asked his permission to name the new building in his honor. Instead, the governor persuaded them to name it Nassau Hall, "for the glorious King William the Third of the illustrious House of Nassau," who was highly regarded by dissenters as a champion of religious freedom and political liberty.
Although only six of Belcher's books have survived, he is still honored as the library's oldest benefactor. When Firestone Library was built in 1948, his coat of arms was carved in stone over the main entrance along with those of the University. Belcher's full-length portrait and the paintings of the 10 English monarchs were destroyed during the Revolution.