Frank Issac Mason was admitted to the Minnesota bar on December 2, 1895, at age thirty-three. He set up shop in Minneapolis and had a general practice until 1928, when he moved to Pine City for three years. In the early 1930s he began to lose his eyesight; surgeries were unsuccessful, and he was forced to cease practice. He died on December 29, 1939, at age seventy-seven.
He seems to have been a man who became the subject of colorful stories and impressions. In a memorial for the Hennepin County Bar Association in 1940, a longtime client was quoted: "You know I have always been outspoken myself on the witness stand and was never afraid. But sometimes I was scared because he used to talk to the court like a bear, tell 'em what the law was, wind up with the argument to say 'That's all.' then he would pick up his book in books and files. He didn't kill much time in court."