Garfield became a law professor and eighth president of his alma mater, Williams College in Massachusetts, and taught at Princeton University as well. While at Princeton, he befriended future president Woodrow Wilson. In 1917, President Wilson asked him to run the nation's Federal Fuel Administration, where he was responsible for coordinating the production and price of fuel during World War I.
He married his second cousin, Belle Hartford Mason, and had four children by her.
He is buried in the faculty cemetery at Williams College.