Masterson became a assistant marshal in Dodge City in June 1878. Other members in the police department included Charles Bassett and Wyatt Earp. He also worked as a deputy sheriff of Ford County under his brother, Bat Masterson.
In November , 1879, Masterson was promoted to marshal of Dodge City. He lost the job with a change in the city government on 6th April, 1881. Ten days later he shot Al Updegraff. As a result of this incident Masterson was ordered out of Dodge City.
Masterson moved to Guthrie before becoming deputy sheriff of Logan County. He also took part in a gun battle with b on 1st September, 1893.
James Masterson died of consumption on 31st March, 1895.
Yesterday morning about 3 o'clock this peaceful suburban city was thrown into unusual excitement, and the turmoil was all caused by a rantankerous cow boy who started the mischief by a too free use of his little revolver.
In Dodge City, after dark, the report of a revolver generally means business and is an indication that somebody is on the war path, therefore when the noise of this shooting and the yells of excited voices rang out on the midnight breeze, the sleeping community awoke from their slumbers, listened a while to the click of the revolver, wondered who was shot this time, and then went to sleep again. But in the morning many dreaded to hear the result of the war lest it should be a story of bloodshed and carnage, or of death to some familiar friend. But in this instance there was an abundance of noise and smoke, with no very terrible results.
It seems that three or four herders were paying their respects to the city and its institutions, and as is usually their custom, remained until about 3 o'clock in the morning, when they prepared to return to their camps. They buckled on their revolvers, which they were not allowed to wear around town, and mounted their horses, when all at once one of them conceived the idea that to finish the night's revelry and give the natives due warning of his departure, he must do some shooting, and forthwith he commenced to bang away, one of the bullets whizzing into a dance hall near by, causing no little commotion among the participants in the "dreamy waltz" and quadrille. Wyatt Earp and James Masterson made a raid on the shootist who gave them two or three volleys, but fortunately without effect. The policemen returned the fire and followed the herders with the intention of arresting them.
The firing then became general, and some rooster who did not exactly understand the situation, perched himself in the window of the dance hall and indulged in a promiscuous shoot all by himself. The herders rode across the bridge followed by the officers. A few yards from the bridge one of the herders fell from his horse from weakness caused by a wound in the arm which he had received during the fracas. The other herder made good his escape. The wounded man was properly cared for and his wound, which proved to be a bad one, was dressed by Dr. T. L. McCarty. His name is George Hoy, and he is rather an intelligent looking young man.
Jim Masterson, a first day settler of Guthrie and a well known figure about town, died last night about 11 o'clock. The cause of his death was quick consumption. He was conscious to the last. He was even out Saturday; but last night about 10 o'clock he called to have some of his friends come to see him, and died an hour later.
The deceased was at one time a well known figure in western Kansas. He was one of the marshals of Dodge City during its cowboy days and was reputed to be a brave man. He came to this city the first day and has been acting as deputy marshal since. He was considered here the bravest of all the marshals. Whenever a big raid was to be made on any stronghold of outlaws, like that at Ingalls,13 he was always asked to be one of the party.
When every man would flinch, he would still be found in the front rank. Every man has his virtues and his faults. Jim Masterson was a man who never went back on a friend, and never forgot an obligation. He never pretended to keep up the conventional social amenities; but yet there was a man whom money could absolutely never make break a trust, and who would have done a kind act to a man on the gallows after all the world had given him the cold shoulder, and where there was no chance of any personal reward. Many who walk the conventional paths of social life are not as honorable in their obligations to their fellow men as he was. He was so proud that in his last moments he would not let his condition be known to his relatives. He is a brother of Bat Masterson, a man of national reputation as a backer of athletic sports, and quite rich, but he would not apply to him for aid.