He studied at the Polytechnic institute of Brooklyn, graduated at Rutgers College in 1870, and was admitted to the bar in 1875 in New Brunswick, New Jersey, where he taught in the Rutgers College grammar school from 1876 to 1879.
His grandfather, Frederick Frelinghuysen (1753-1804), was an eminent lawyer, one of the framers of the first New Jersey constitution, a soldier in the War of Independence, and a member (1778-1779 and 1782-1783) of the Continental Congress from New Jersey, and in 1793-1796 of the United States senate; and his uncle, Theodore (1787-1862), was attorney-general of New Jersey from 1817 to 1829, was a United States senator from New Jersey in 1829-1835, was the Whig candidate for vice-president on the Clay ticket in 1844, and was chancellor of the university of New York in 1839-1850 and president of Rutgers College in 1850-1862.
Frederick Theodore, left an orphan at the age of three, was adopted by his uncle, graduated at Rutgers in 1836, and studied law in Newark with his uncle, to whose practice he succeeded in 1839, soon after his admission to the bar.
This action was opposed by the church of New York City, and partly through this difference and partly because of quarrels over the denominational control of King's College (now Columbia), five members of the Coetus seceded, and as the president of the Coetus was one of them they took the records with them; they were called the Conferentie; they organized independently in 1764 and carried on a bitter warfare with the Coetus (now more properly called the American Classis), which in 1766 (and again in 1770) obtained a charter for Queen's (now Rutgers) College at New Brunswick.
The colleges and institutions of learning connected with the Church are: Rutgers, already mentioned; Union College (1795), the outgrowth of Schenectady Academy, founded in 1785 by Dirck Romeyn, a Dutch minister; Hope College (1866; coeducational) at Holland, Michigan, originally a parochial school (1850) and then (1855) Holland Academy; the Theological Seminary at New Brunswick (q.v.); and the Western Theological Seminary (1869) at Holland, Michigan.