Born in 1843 in Ohio to Scottish immigrants John and Isabella (Brock) McGregor, Malcolm McGregor arrived in the small settlement of Carthage in March 1866. He had left Ohio, stayed with a sister and brother of his in Iowa, taught school there for one term before moving on to Kansas City, Missouri. He apprenticed as a lawyer until he was admitted to the bar. He rode a train from Lexington, Mo. to Ft. Scott and began walking to this area, a journey that took two days to complete. When he arrived in Carthage there were only two other attorneys, who ended up deciding not to stay in the area.
Carthage, by 1868, had 206 taxpayers who signed a petition that Malcolm McGregor wrote and presented on their behalf to the County Court to have the settlement incorporated as a town, which was granted. When a school board was formed, he was the elected secretary. He also was married in 1868 to Olive Stephenson. He wrote the letter to Washington that asked for a post office to be established in Carthage and that George Radar be appointed as Postmaster. Both requests were quickly granted. By 1873 he was appointed a district judge for Carthage and City attorney. In 1878 he chaired the newly formed Old Settlers Association and spoke at its first gathering.
He was elected a circuit judge in 1880, serving two six-year terms, for Jasper, Newton, McDonald and Lawrence counties. In 1888 he was sent to preside over a trial in Christian county of one of the notorious Bald Knobbers, John Matthew, who was found guilty of murder and hanged.
In 1901 he authored the Biographical Record of Jasper County and did so with a firsthand knowledge of many of the subjects.
Malcolm McGregor contracted pneumonia in late spring 1923 and died on May 2, 1923. He was laid to rest at Park Cemetery with his wife who had died in 1882 and one of his daughters who had predeceased him.