After a clerkship, thirty-one year old Thomas Jefferson McDermott was admitted to the bar on April 6, 1892, but feeling inadequately prepared for practice, he entered the University of Minnesota Law Department and graduated with a LL.B in 1895, followed by a LL.M. in 1897.
An active Democrat, he ran for attorney general in 1904 but lost to Edward T. Young by a 2: 1 margin. For the next thirty-five years he was engaged in law and politics in St. Paul. He died on November 17, 1939, and the next day the "St. Paul Dispatch" carried his obituary.
Like others lawyers of this period, he helped fund the publication of local history books which, in return, carried their personal profiles. In a self-portrait in Hiram F. Stevens' "History of the Bench and Bar of Minnesota" (1904), he listed seven of his cases which he considered of "paramount importance" to the profession. One was a libel suit he brought against a credit company for categorizing him "slow in the payment of his bills." When its demurrer was overruled, the defendant appealed to the state supreme court. In one of his last rulings, Justice Mitchell sided first with McDermott but, after reconsideration, dismissed his action. McDermott v. Union Credit Co., 76 Minn. 84 (1899), is posted in the Appendix.