James McCosh was the first president since John Witherspoon who was not an alumnus of the College of New Jersey. Many similarities have been noted between the two men. Both were born in Scotland and graduated from the University of Edinburgh. Witherspoon was inaugurated in 1768, and McCosh was inaugurated one hundred years later in 1868. They died one hundred years apart, almost to the day, and like all presidents until Woodrow Wilson, both were ministers.

McCosh was born April 1, 1811 on a farm in Ayrshire, Scotland. His father, who died when James was nine, had decided that he should be educated for the ministry. McCosh attended Glasgow University and then Edinburgh University. In Edinburgh he joined debating societies, discussing such issues as theology and the power of patronage. He sided with several others in believing that the major landowners should not have the final say on who became the minister of a congregation. This issue would resurface later. Inspired by his professor, Thomas Chalmers, McCosh and other students went to the poorer districts of Edinburgh to preach and do missionary work. He also began to study philosophy and created the groundwork for what would become his most noted published work , The Method of Divine Government, Physical and Moral. Licensed to preach in 1833, his first assignment was the Abbey Chapel in Arbroath; his second at Brechin in Forfarshire, where he met his wife, Isabella Guthrie. The two were married in September 1845. In 1843 "The Disruption" occurred when McCosh, along with one-third of his fellow ministers, left the security of the established Church of Scotland to begin the Free Church of Scotland. The rebellion was caused by the increased interference of Great Britain's central government in church affairs, with ministers being settled in parishes against the will of the people.

McCosh also disagreed with the lack of weight given to supernatural powers in John Stuart Mill's System of Logic and wrote The Method of Divine Government, Physical and Moral in response. The work received much recognition and led to his appointment to the chair of logic and metaphysics at Queen's College, Belfast. He spent 16 years in Ireland, published several other works, and became well known in the English-speaking world. He was one of the few clergymen who agreed with the theory of evolution, albeit within limits. He taught that it served "to increase the wonder and mystery of the process of creation." His published lecture on this subject was The Religious Aspect of Evolution.

McCosh was offered and accepted the presidency of the College of New Jersey in 1868. He found an institution that was in need of repair after the turbulence caused by the Civil War, and McCosh, an expert fundraiser, undertook great improvements. He added distinguished faculty, increased the size of the student body, developed elective courses, bought scientific equipment, founded schools of science, philosophy, and art, added buildings, and enhanced the campus landscape. McCosh believed that the body as well as the mind should be cultivated, and on his arrival, he announced that he would build a gymnasium. When the Bonner-Marquand Gymnasium was completed a year later, it was the first college gymnasium built in the United States. McCosh also added Chancellor Green Library (1873), the Marquand Chapel (1881), and the Observatory (1869), among other buildings, while increasing the treasury by three million dollars. During his presidency The Daily Princetonian, The Tiger, and the Bric-a-Brac were founded, and extracurricular activities that evolved into the Triangle Club, the Glee Club, and intercollegiate football were initiated. With all these accomplishments to his credit, it is no wonder that McCosh referred to the College of New Jersey as "me college." His students affectionately referred to him as "Jimmie," and his wife also took a personal interest in students by caring for those who were ill. Four years after McCosh retired, the trustees erected the College's first infirmary and named it in her honor. McCosh ranks among Princeton University's most successful presidents, setting his institution well on the path to university status.

The McCosh records are arranged topically. Materials of note during his presidency include information about commencements, the regulation of liquor in the town of Princeton, and his request to stop teaching while serving as president. Pre-presidency highlights include the certificate appointing McCosh as the first minister of the church of Brechin, a farewell letter signed by his associates and friends in Ireland, plans for the Queen's College Library, and invitations and programs from his inauguration. The correspondence is arranged alphabetically by correspondent, with foreign letters at the end of the run. Letters from McCosh with unidentifiable addressees are filed under McCosh in chronological order. This series also contains numerous clippings and articles of a biographical nature. Also of interest are a large number of images, including photographs of McCosh and the construction of his Prospect Street house.