King received training to become a house painter in Boston, Massachusetts, which became one of his many occupations. King had pursued several vocations before beginning his artistic career. He painted houses, made frames, decorated carriages and made mathematical and navigational instruments.
He made a miniature portrait painting Reverend Ezra Stiles in 1770, which is now part of the Metropolitan Museum of Art"s collection.
Stiles, who performed King"s marriage ceremony, went on to become the president of Yale College. The following year he painted Stiles portrait on canvas.
King taught artists Ann Hall, Charles Bird King, Edward Greene Malbone, and Washington Allston. Malbone had been encouraged by King to become an artist.
Hall visited Newport to receive lessons from King.
He created a transparency for the Rhode Island State House in 1783, which was "probably" illuminated from torches placed behind the large transparency.
Married Amey Vernon, August 26, 1770. Married second, Sarah Ward, November 1795.