Haret was born in Iaşi, Moldavia, to an old Armenian family, and showed an early talent for mathematics, publishing two textbooks when he was still a high school student. In 1869 he entered the University of Bucharest, where he studied physics and mathematics. In 1870, while a student in his second term, he became teacher of mathematics at Nifon Seminary in Bucharest, but quit the following year in order to continue his studies. In 1874, at age 23, he graduated with a degree in physics and mathematics. After graduation, Haret won a scholarship competition organized by Titu Maiorescu and went to Paris in order to study mathematics at the Sorbonne. There he earned a mathematics diploma in 1875 and a physics diploma in 1876. Two years later he earned his Ph.D. by defending his thesis, Sur l’invariabilité des grandes axes des orbites planétaires, in front of examiners led by Victor Puiseux. In this work he proved a result fundamental for the n-body problem in astronomy, the thesis being published in Vol. XVIII of the Annales de l'Observatoire de Paris. Haret was the first Romanian to obtain a Ph.D. degree in Paris. After his return to Romania in 1878, Haret abandoned scientific research and dedicated the rest of his life to improving Romanian education, which was heavily underdeveloped at the time, both as professor and as politician. He was appointed professor of rational mechanics at the Science Faculty in Bucharest. The next year, Haret became a correspondent member of the Romanian Academy, receiving full membership in 1892. He kept the professorship at the Science Faculty until his retirement in 1910, when he was followed as professor of mechanics by Dimitrie Pompeiu. From 1882 he was also a professor of analytical geometry at the Bridges and Roads' School in Bucharest. After retirement, Haret occasionally lectured at the informal People's University. Haret was the Minister of Public Education in three liberal governments, between 1897–1899, 1901–1904 and 1907–1910. As Minister of Education he ran a complete reform, basically building the modern Romanian education system.
Haret’s major scientific contribution was made in 1878, in his Ph.D. thesis Sur l’invariabilité des grandes axes des orbites planétaires. At the time it was known that planets disturb each other’s orbits, thus deviating from the ellipticmotion described by Johannes Kepler’s First Law. Pierre Laplace and Joseph Louis Lagrange had already studied the problem, both of them showing that the major axes of the orbits are stable, by using a first degree approximation of the perturbing forces. In 1808 Siméon Denis Poisson had proved that the stability also holds when using second degree approximations. In his thesis, Haret proved by using third degree approximations that the axes are not stable as previously believed, but instead feature a time variability, which he called secular perturbations. This result implies that planetary motion is not absolutely stable. Henri Poincaré considered this result a great surprise and continued Haret’s research, which eventually led him to the creation of chaos theory. Félix Tisserand recommended the extension of Haret's method to other astronomic problems and, much later, in 1955, Jean Meffroy restarted Haret’s research using new techniques. Soon after his return to Romania, Haret abandoned research, focusing for the rest of his life on teaching and, as Minister of Education, on the reform of the education system. He only published an article on the secular acceleration of the Moon in 1880 and one on Jupiter’s Great Red Spot. In 1910 he published Social mechanics, which used mathematics to explain social behaviour.
