Oliver helped found a law firm

In the summer of 1864, Holmes went back to his parent's house in Boston where he continued to work on his philosophical argument with the help of his friend William James, wrote poems, engaged in philosophical discussion, and thought about re-enlisting. However, in the fall, when it became apparent that the war would soon come to an end, Holmes enrolled in Harvard Law School after, as he subsequently recalled, being "kicked out of the law" by his father. After a year of attending lectures there, reading several theoretical books, and working as Robert Morse's cousin for a year as a secretary. After spending a lengthy time in London to finish his studies, he was admitted to the bar in 1866 and started practicing law in Boston.

Oliver Wendel Holmes Jr. left Harvard and moved to England. After his return, he concentrated on his legal career and helped establish the Shattuck, Holmes, and Munroe law company. After graduating from law school, Holmes continued to devote his free time to furthering his knowledge of his field.

For fifteen years, Holmes has worked as a commercial and admiralty lawyer in Boston. A new version of Kent's Commentaries, which serves practitioners as a compendium of case law at a time when formal reports are uncommon and challenging to get, was prepared during this time. He also served as editor of the New American Law Review during this time. In a collection of lectures that were assembled and published as The Common Law in 1881, he condensed his laboriously attained understanding.