In the autumn of 1815, Dr. Oliver was appointed to deliver a course of chemical lectures before the medical class at Dartmouth College. Although he had thus far pursued the study of chemistry as a collateral branch of medical science, he felt warranted in accepting the appointment, without, however, proposing to himself a more permanent position in this department.
In 1817, he was married to Miss Mary Robinson Pulling, the only daughter of Edward Pulling, Esq., an eminent barrister of Salem, and almost immediately went again to Philadelphia to avail himself of the advantages of that seat of medical learning, returning to Salem in the spring of 1818.
In the following year he was induced to undertake, in connection with the Hon. John Pickering, the preparation of a Greek lexicon, a work involving much labor and research, and the larger portion of which fell to his lot. Although mainly based on the Latin of Schrevelius, many of the interpretations were new, and there were added more than two thousand new articles. The magnitude of the task and its successful accomplishment at once raised him to a conspicuous rank among the scholars of his day.
In the summer of 1820 he accepted an appointment to the professorship of the Theory and Practice of Medicine, and of Materia Medica and Therapeutics in Dartmouth College, where he delivered his first course of lectures in the following autumn. He was also made Professor of Botany, and his lectures upon Physiology were among his most valuable contributions to medical literature. He took up his permanent residence in Hanover, in August, 1821, and from this time to the close of his connection with the college he was most faithful to all its interests. In 1825 he was appointed to the chair of Intellectual Philosophy in the Academical department of the college, a position which he filled with the ability that distinguished him elsewhere. The address delivered by him on the occasion of his induction into this professorship, upon the "Comparative Importance of the Study of Mental Science," was thus far, perhaps, his most successful literary effort. Clear, comprehensive, and abounding in passages of remarkable beauty and force, it established the reputation of its author both as a writer and a metaphysician.