The Pruyn family of Albany, New York was one of the oldest and most esteemed Dutch families in New York, and at the time of Robert's birth there, had resided in Albany for over two centuries. Pruyn earned an A.B. in 1833 and Master in 1836 from Rutgers Academy and began the practice of law in Albany. Active in the state militia, he was named Judge Advocate General in 1841, serving until 1846, and again in 1851. In 1866, he was the Conservative Union candidate for Lieutenant Governor of New York. He died suddenly in 1882 in Albany. His remains are interred at Albany Rural Cemetery.