He graduated from the University of Michigan Law School in 1867 and built a very successful practice in Detroit, frequently arguing cases before the Supreme Court of the United States.

He was a member of Democratic National Committee from Michigan 1880–1885, and was an early supporter of the candidacy of Grover Cleveland for President in 1884.

[1] After the election, Cleveland offered Dickinson a position on the recently created Civil Service Commission, but he declined.

However, in 1887, Dickinson accepted the appointment as United States Postmaster General, serving from January 6, 1888, until the end of Cleveland's first term in 1889.

Dickinson refused to use federal forces to break the strike and instead modified the distribution routes so that postal deliveries could continue.