Alfred Brunson McCalmont was born at Franklin in Venango County, Pennsylvania on April 28, 1825, the fourth of five children and third son of Alexander and Elizabeth Hart Connely McCalmont. He attended from an early age the local Latin School that Reverend Nathanial Randolph Snowden kept in Franklin and in 1839 entered Allegheny College. He soon withdrew and entered Dickinson College in Carlisle, Pennsylvania, where, coincidentally, Snowden had been a member of the board of trustees from 1794 to 1827, when it was under Presbyterian auspices. McCalmont entered with the class of 1844 and was elected to the Belle Lettres Society. He graduated joint top of his class and began law studies at home in Franklin under his sister's husband, Edwin Wilson and his own father, who was then a Pennsylvania District Judge.
He interrupted his studies for a time to travel west with a friend to Iowa. He soon changed his mind and drifted home again, teaching school in St. Louis, Missouri to help pay for his journey. He passed the bar back in Franklin 1847 and relocated to Pittsburgh. There he helped his Dickinson classmate, Thomas Johnston Keenan, edit the Pittsburgh Legal Journal and a Democratic newspaper called the Daily Union. His political work brought him an appointment as the prothonotary of the western district of the Pennsylvania supreme court and then in 1858 the Attorney-General in President Buchanan's cabinet, Jeremiah Black, appointed him as one of the new Assistant Attorney-Generals of the United States. He served until 1860 when the new administration took office. At the outbreak of the Civil War, he helped raise a company of volunteer infantry in Franklin. The unit became a part of the 142nd Pennsylvania Volunteer Infantry and McCalmont was appointed a lieutenant-colonel in September 1862. The regiment's rigorous baptism of fire came at Fredericksburg in December 1862 where it lost 250 men killed and wounded. Chancellorsville saw fewer losses in April 1863 while at Gettysburg in July the unit was heavily involved on the first day and in all lost its colonel and fourteen others killed, with 126 wounded and eighty-four missing or captured. McCalmont then took command of the 142nd until April 1864 when he was detailed to take command of the new 208th Pennsylvania Infantry then being recruited and organized. Ready for active service in September, the 208th joined the final campaigns of the war, including the seige and storming of Peterburg and the Appomattox campaign. McCalmont had already, on March 13, 1865, been awarded the brevet of brigadier general for his service throughout the war and he was able to lead the 208th in the Grand Review victory celebrations in Washington on May 23, 1865. Returning to Franklin, he resumed building a thriving law practice. He ran unsuccessfully for Congress in 1866 and toyed with the idea of bid for governor of the state in 1872.
During his time in Pittsburgh, McCalmont had met Sarah Frances Evans and they were married in the Trinity Church on April 28, 1853. The couple had three children, two daughters and a son. In early 1874, a tumor developed near McCalmont's ear and in May he travelled to Philadelphia for its removal. Following the operation, infection set in and on May 7, 1874, Alfred Brunson McCalmont died. His body was returned to Frankin where he was buried. He was forty-nine years old.