In 1878, a year after he was admitted to the bar, Darius Morgan became the associate of John A. Lovely, a future supreme court justice, in Albert Lea. He practiced law with Lovely and his younger brother, Henry A. Morgan, for more than a decade. Seeking greater professional opportunities, he moved to Mankato around 1891, and a year later to Minneapolis where he practiced briefly with William H. Eustis, then with William Edward Hale, a leader of the city bar.
From the outset of his legal career he was involved in Republican politics. He served one term in the state house, 1889-1890, and one in the senate, 1895-1899. In 1896, however, he broke from the party to form the Silver Republicans.
In the fall of 1898, he left his firm and went "in house" as General Counsel to the Northwestern Telephone Company, with responsibilities over its legal affairs in seven Midwest and Southwestern states.
He died on April 27, 1903, at age 49. In a memorial presented at the annual convention of the Minnesota State Bar Association in 1904, he was recalled as "logical, industrious, discriminating, fair-minded, and loyal to his clients' cause." One particular accomplishment was noted: "More than any other man he [was] responsible for producing the arguments which have formed the basis for the pioneer decisions in telephone cases in Minnesota. Had he been connected with no other litigation, that would have made him prominent."