O'Donovan was a self-taught artist who studied with "no on particularly." His early artistic pursuits, whatever they may have been, were interrupted by the Civil War during which he served in the Confederate army. After the war, in 1867, he moved to New York where, as might be expected, his early years were not easy. Somewhat ironically, he found a major stumbling block to his success to be the National Academy. This is clearly expressed in a letter he wrote to his sister in 1871. Describing the plight of young artists in the city, O'Donovan reported: "If they are painters and send a picture to the Exhibition of the Academy this class of what we term `Old fossils'--to which [John Q. A.] Ward belongs, will hang it in such a manner as to kill it. These men `run' the Academy, they `run' the clubs, and have formed themselves into a `ring' for the purpose of keeping to themselves all the art patronage of the Country, and I believe I am the only young man in the City who has ever been bold enough to fight them. I have done it and I have succeeded in spite of them and today I am stronger than any of them, and I will make them feel it before another year has passed."
Before the decade was out, O'Donovan was not the only artist fighting the "fossils," and in 1877 he joined with other artists to form the Tile Club, an informal group, independent of the Academy. O'Donovan was also an early exhibitor with the Society of American Artists which was formed as a direct result of disagreements among the members and officers of the Academy.
Nevertheless, O'Donovan did not spurn the Academy completely. He began sending sculptures, mostly busts, to the Academy's annuals in 1874, a practice he continued through the following decade, and he accepted election to Associate membership in 1878. But disappointment seems to have been all that he gained from his affiliation with the Academy. Following the 1874 annual, he wrote his sister that his work, a bust of Peter Gilsey, "was not mentioned by a single one of the so-called critics. . . . Nor so far as I could see during repeated visits to the Academy, did it attract the attention of the visitors." The rather conservative rules of the Academy caught up with him, too, when he was dropped from the membership rolls in 1894 for failing to participate in the Academy's annuals in the preceeding years. While the situation was rectified two years later when his membership was reinstated, O'Donovan was never elected to full National Academician and there is no evidence that he pursued or coveted that status.
To some degree, this may have been due to his distaste for the conservatism of the Academy, but it may have also been related to the success he finally achieved, despite the Academy, in the late 1870s. By that time, he had become a "society artist." "Gay and brilliant throngs of people exilerate me," he wrote. He gained a reputation for his busts of fellow artists such as Winslow Homer (Metropolitan Museum of Art) and Robert Swain Gifford (The Century Association) as well as those of other famous Americans. During the 1880s he turned to painting, especially in watercolor, but in the following decade he returned to sculpture as his preferred medium. His military monuments, such as statues of Washington for the Trenton Battle Monument and the Peace Monument at Newburgh, New York, as well as other major memorial commissions insured his fame and financial security for the remainder of his life.
His best known public sculpture is the high relief figures of Lincoln and Grant who ride horses modeled by Thomas Eakins on the inside of the Soldiers' and Sailors' Memorial Arch in Brooklyn. The project was completed during the early 1890s, but the relationship between the two artists, O'Donovan and Eakins, went beyond that of mere collaborators. In 1879, O'Donovan had been among the artists sent to Philadelphia by the Society of American Artists to defend Eakins' painting The Gross Clinic, and in 1891 he accompanied Eakins to the 72nd birthday of Walt Whitman. Furthermore, the two artists proved their friendship by producing portraits of one another (both unlocated). They were kindred spirits, New York and Phildelphia counterparts in that struggle with academic tradition which is so much a part of the story of late 19th-century art. O'Donovan's part in that struggle was noted by the critic Sadakichi Hartmann who characterized his sculpture as part of "the new school" which sought to translate form into "fresh and spirited compositions of a more pictorial tendency and an individuality of touch."
At O'Donovan's death the Council of the National Academy paid tribute to him at their monthly meeting by giving him a epithet he most certainly would have appreciated. His work, the minutes of that meeting state, was "distinctively American."
