Nathaniel, brought up to succeed to his father's business, received only an elementary education. At the age of fifteen, with his brother and a friend, he undertook a course of study in drawing, entirely without instruction.
In 1817, after three years as apprentice to an engraver, Jocelyn became a partner in a new enterprise, the Hartford Graphic & Bank Note Engraving Company; and later, with M. I. Danforth, he founded the National Bank Note Engraving Company. His share in the labor of the company, which was confined to the lettering, hardly afforded sufficient outlet for his talents, and at the age of twenty-five he began painting portraits, at first in Savannah, Georgia, and later in New Haven. He had an unusual talent for securing a likeness, his brush-work was vigorous and his modeling strong and graceful, and there was an increasing demand for his work. He was thirty when several of his portraits, hung at the first exhibition of the National Academy, won favorable comment.
In 1829 Jocelyn went abroad, resided for a few weeks in London, and traveled in France and Italy with Samuel F. B. Morse. Upon his return, he established himself in a studio in New Haven and divided his time between business and his art.
For many years he was head of the art department of the American Bank Note Company, resigning in 1865. Investments in real estate and enthusiastic attempts to develop new sections of the city occupied his energy and drew him for a time out of his studio; but during the years of depression that followed the panic of 1837, he was in serious financial difficulties, and the burden he was carrying made it necessary for him to earn money with his brush. In 1844 he received the gold palette for the best portrait exhibited in Connecticut.
In 1849, after a fire had destroyed his studio, Jocelyn removed to New York; but he was soon back in New Haven, and most of his painting was done there. He taught many pupils, including Thomas Rossiter and William Oliver Stone. August Street, who provided the original building of the Yale School of the Fine Arts, frequently stated that his gift was made largely as a result of Jocelyn's suggestions. The artist had his studio in Street Hall during the last fifteen years of his life, and some of his best work is now on exhibition in the gallery of the school. His celebrated portrait of Cinqué, leader of the Amistad Africans, hangs in the building of the New Haven Colony Historical Society, where there is also a portrait of Jocelyn painted by Harry Thompson.
Jocelyn was a wide reader and preserved a variety of interests down to the time of his death. In his old age, he left upon all who saw him the same impression of remarkable vitality that he had given in his prime.
Jocelyn died on January 13, 1881, in New Haven, Connecticut.
Jocelyn was a member of the Connecticut Academy of Arts and an honorary member of the National Academy of Design. He declined an election to honorary membership in the Philadelphia Art Union because the society had offended his antislavery sentiments.
Jocelyn was said to be a very handsome, lithe, graceful figure, with a brilliant complexion and mild blue eyes.
Nathaniel Jocelyn married on July 5, 1818, Sarah Atwater, daughter of Capt. Samuel Plant, of New Haven. They had seven children, one son and six daughters, the son Isaac dying in childhood.