He served as district attorney of Union County between 1821 and 1824; he was then clerk of the Dauphin County commissioners from 1824 until October 23, 1827, when he was appointed an associate judge of the county court. Seen by most as honest and modest, McKinney did not acquire more than a comfortable income but poured his attentions into the study of the law. He published profusely on the subject, including the well known McKinney's Digest of the Laws of Pennsylvania as well as The Pennsylvania Justice of the Peace in two volumes in 1839 and The American Magistrate and Civil Officer in 1850, among others.
As the son of slaveholders on both sides of his parentage, and as a man who married a daughter of a slave holding family, McKinney's main legacy may have been his extensive legal and cultural work with both the African-American population of Harrisburg and the escaped families of the underground railroad that came through the city. He had developed strong anti-slavery views and had been active in the Liberty Party in 1847, serving on the central committee of the party's convention held in Harrisburg. Before and after the passage of the Fugitive Slave Act in 1850, he represented many local African-Americans and runaways from the south in the significantly hostile legal atmosphere of the Pennsylvania capital. He also aided in other ways, helping to found the African-American Second Prebyterian Church on Walnut Street.
He married Rachel Graydon who died on April 12, 1856. Judge McKinney himself died in Harrisburg on December 17, 1867 after having been struck down by a city streetcar three days before. He was buried in the Harrisburg Cemetery. Mordecai McKinney was seventy-one years old.
Almost immediately McKinney, a fellow Dickinson College alumni of his rival McAllister, established a stake out arrangement with members of the Harrisburg Anti-Slavery Society (HAS) outside of the slave commissioner’s house. As the leader of this HAS committee, McKinney became the “antislavery mayor” of Harrisburg. The committee was responsible for setting up a neighborhood watch program to track the activities of his younger nemesis. All of the information gathered bout McAllister was relayed back both HAS and Judge Pearson so that they could be prepared to take legal action against the slave commissioner.
Died December 17, 1867.
Mordecai McKinney, son of Mordecai McKinney and Mary Chambers, daughter of Colonel William Chambers, was born near Carlisle, Pennsylvania. His parents resided on a farm and were of that numerous body of Scotch-Irish who were the first settlers of Cumberland Valley. His early studies were pursued at Dickinson College, where he spent six years, graduating while quite a youth. He began the study of law in the office of Judge Duncan, of Carlisle, and after his removal to Harrisburg, completed his studies, in the office of Hon. Amos Ellmaker, Attorney General of the State, and was admitted to the bar in May, 1817. In 1821 he was appointed District Attorney of Union county, and October 12, 1827, Governor Shultze appointed him one of the associate judges of Dauphin county, Pa. He served five years. Subsequently Judge McKinney turned his attention to the compilation of law books and published "McKinney's Pennsylvania Tax Laws,” and other works of value to the profession. Later still in life he published a volume of labor, research and worth, entitled, "Our Government," an explanatory statement of the system of government in this country in its various departments of the State and the Nation. He was a man of extended and accurate knowledge in his profession, an honest and conscientious [counselor], but so modest and retiring that he shrank from the public contests of the bar.
Mr. McKinney married Rachel Graydon, daughter of William Graydon. Her death occurred at Harrisburg, April 12, 1856. Mr. McKinney principally wrought his mission in the world by his Christian life and character. His life as a man and a citizen was completely transfused by his religion, sanctified and elevated by it. He was one of the most guileless of men, a man of sterling honesty and conscientiousness, and was remarkably free from selfishness and pride, spending all his years in comparative poverty, no more contented, trusting and happy man walked the streets of the city. He was a friend to all that was venerable and good, a defender of law, and a supporter of all that promised to promote the welfare of society.
Though he could give but little he was distinguished as a philanthropist, giving what is often far better than money, time and attention and his most hearty sympathy. A true-hearted man, he "counted nothing foreign to him that was human," giving in genuine unselfishness a faithful and earnest devotion to the outcasts and Pariahs of society. He knew no ambition beyond the simple doing of right, and though so lowly and unassuming in all things else, in this he was as brave a man as ever faced an enemy. No notions of policy or of expediency ever swerved him from his course. He was the friend of the slave, of the poor, of the despised, and his loyalty to their rights and wants merited universal admiration. And touching as was the tribute to his worth when on the day of his burial, the officers of the court and members of the bar at their head, the president judge passed beside his coffin, taking their last and silent look and giving their unspoken farewell to their old friend and associate who died as poor in worldly goods as he was morally great, it was by no means so noble and so impressive a testimony to his goodness and worth as when the long procession of parents and children from the colored population of this city passed, and with the touching eloquence of sobs and tears told all, that they had lost their best earthly friend.
It is, however, as a devout Christian that Mr. McKinney will chiefly and permanently live in the history of the Church. For half a century he was an active member of its communion, for fourteen years a member of its Board of Trustees, and for thirteen years a Ruling Elder. The Presbyterian Church was his by descent, by education, by love of its doctrines and order. It was a pride and a pleasure to him to sit, as he was permitted to do, in her various courts, the Presbytery,
the Synod and the General Assembly.
Judge McKinney was a great student of the Bible. His brethren of the bar were wont to find open on the table where lay his commentaries on human law, the volume of Divine Law, and with its contents he was more familiar than with any work of human origin. He was a theologian of the Scriptures.
For many years most of his active Christian labors were given freely, and as the chief reward the pleasure of doing good, to the colored people of the city. He sought no public notice. He was ever at his post. His life was a life with God. A life of kind thoughts, pious deeds, charity toward men and of trust toward God. It was closed by a calm and quiet death of entire trust in the Great Redeemer, for whose speedy second coming he had longingly waited. His death was the result of injuries from a street car, and when he was told by his pastor that in a few hours he would stand amid the scenes of eternity, he heard the announcement with all the composure and calmness of one who hears of the most common event of life. The half a century of prayers, labors, counsels and godly living that Judge McKinney gave to this Church are of inestimable worth.