A graduate of George Washington University Law School in Washington, D.C., in 1897, Henry Clay Carlson moved to Albert Lea, Minnesota, where he practiced for about 20 years. In 1919 he moved to Minneapolis where he joined a small firm headed by Henry Fowler. There he practiced another 20 years before retiring in 1939. After his death on October 7, 1944, at age 72, a former partner, Fred Furber, recalled him at memorial proceedings of the Hennepin County Bar Association:
"Concerning the contribution which Henry Clay Carlson made to the bar, it may be said to an unusual degree he possessed a logical mind and retentive memory. He was by nature methodical and painstaking, with a great gift of expression. In his early years of practice in southern Minnesota as a country lawyer, he acquired a fundamental store of knowledge, general information and familiarity with legal precedents and procedure that to an unusual degree aided and back-grounded his great legal talents during the twenty years of his practice in Minneapolis before his retirement."