[3] In 1850, he entered Harvard Law School, where his close friend and roommate was Edward L. Pierce.
In 1855, he was appointed Corporation Counsel under Mayor George Hall and advised him on the consolidation of Brooklyn with Williamsburgh.
In 1866 he formed a partnership with Joshua Van Cott, with law offices in New York City.
In 1873, he was an unsuccessful Republican candidate for the New York Supreme Court, but a year later Governor Dix appointed him to fill a vacancy as Brooklyn District Attorney.
[1] Winslow was one of the founders of the Long Island Historical Society, and for many years was its secretary and a director.