Going to Europe in 1835 Healy studied under Baron Gros in Paris and in Rome. He received a third-class medal in Paris in 1840, and one of the second class in 1855, when he exhibited his "Franklin urging the claims of the American Colonies before Louis XVI."
Among his portraits of eminent men are those of Daniel Webster, Henry Clay, John Calhoun, Arnold Henry Guyot, William H. Seward, Louis Philippe, and the presidents of the United States from J. Q. Adams to Ulysses Grant this series being painted for the Corcoran Gallery, Washington, D.C.. Healy also painted a very famous presidential portrait of Abraham Lincoln in 1877. This painting was based on his 1868 painting The Peacemakers.
His father was an Irish captain in the merchant marine, and "the Celtic strain ran bright and lovable through the temperament of the son' (Isham). The eldest of five children, Healy, early left fatherless, helped to support his mother. When sixteen years of age he began drawing, and at once fired with the ambition to be an artist. Miss Stuart, daughter of the American painter, aided him in every way, loaned him a Guido's "Ecce Homo", which he copied in colour and sold to a country priest. Later, she introduced him to Sully, by whose advice Healy profited much, and gratefully repaid Sully in the days of the latter's adversity. At eighteen, Healy began painting portraits, and was soon very successful. In 1834, he went to Europe, leaving his mother well provided for, and remained abroad sixteen years during which he studied with Baron Gros, came under the pervading influence of Couture, painted assiduously, and won (1840) a third class medal in the Salon.
His Franklin urging the Claims of the Colonists before Louis XVI gained him a second-class gold medal at the Paris International Exhibition of 1855. This year, also, saw him in Chicago, where he remained until 1869, when he again visited the Continent, painting steadily, chiefly in Rome and Paris, for twenty-one years. His final return to Chicago was in 1892. Healy painted more portraits than any other American artist, and of more eminent men than any other artist in the world. Among his sitters were Pius IX (1871), Lincoln, Grant (1878) Cardinal McCloskey, Louis Philippe ("his royal patron"), Marshal Soult, Webster, Calhoun, Hawthorne, Prescott, Longfellow, Liszt, Gambetta, Thiers, Lord Lyons, and the Princess (now the queen) of Rumania. In one large historical work, "Webster's Reply to Hayne" (1851), now in Faneuil Hall, Boston, there are one hundred and thirty portraits. Healy was remarkably facile, enterprising, courageous, and industrious. "All my days are spent in my painting room" (Reminiscences). His style, essentially French, was sound, his colour fine, his drawing correct and his management of light and shade excellent. His likenesses, firm in outline, solidly painted, and with later glazings, are emphatic, rugged, and forceful. Healy was an honorary member of the National Academy of Design and wrote a delightful book: "Reminiscences of a Portrait Painter".
Among his principal works are portraits of: Lincoln (Corcoran Gallery), Bishop (later Cardinal) McClosky (bishop's residence, Albany), Guizot (1841, in Smithsonian Institution), Audubon (1838, Boston Soc. Nat. Hist.), Comte de Paris (Met. Mus. Of Art, New York), Isaac Thomas Hecker C.S.P., Founder of the Paulist Fathers (North American Paulist Center, Washington, D.C.).
His large group, Webster Replying to Hayne, containing 180 portraits, is in Faneuil Hall, Boston, Mass. He was one of the most prolific and popular painters of his day. He died in Chicago, Illinois, on 24 June 1894.