His father was lawyer Charles Russell Train, who served for many years as attorney general of Massachusetts, and his mother was Sara Maria Cheney.

He ran the two careers in parallel until 1908 when he left the District Attorney's office to open a general law practice in the Mutual Life Building at 34 Nassau Street in New York City.

[4] In 1912, Train, who as a former assistant to New York County District Attorney William Travers Jerome had dealt with Italian criminals who emigrated to the United States and the Black Hand, attended the Cuocolo Trial in Italy against the Camorra, studying that Mafia-type organisation and the functioning of Italian justice.

[5] From 1915 to 1922, Train was in private practice as a lawyer with Charles Albert Perkins while continuing to write, not just novels but short stories, plays, and journalism.

In 1919, he created the popular character of Mr. Ephraim Tutt, a wily old lawyer who supported the common man and always had a trick up his sleeve to right the law's injustices.