He inherited his father's farm west of town along the Chambersburg Turnpike in 1858[4] and was elected to the 36th and 37th United States Congresses (1859 – March 1863, Republican).

[5] McPherson organized Company K of the First Pennsylvania Reserves at the beginning of the American Civil War,[6] and was defeated in the 1862 reelection when his House of Representatives district (Adams, Franklin, Fulton, Bedford, and Juniata counties)[7] was expanded to include opposing Radical Republicans in Somerset County[citation needed] (substituted for Juniata).

After the Battle of Gettysburg, McPherson became an officer of the Gettysburg Battlefield Memorial Association with an office on the corner of Baltimore and Middle streets,[9] and after Congressman Morehead nominated him, Thaddeus Stevens had him appointed as Clerk of the House of Representatives (December 8, 1863 – December 5, 1875).

McPherson was the attorney for the 1893 complaint against the Gettysburg Electric Railway which ended in the Supreme Court case of United States v. Gettysburg Electric Railway Co.[10] McPherson diverted printing contracts away from Radical Republican newspapers and to moderate newspapers instead.

He initially granted a contract to The New Orleans Tribune, a black-owned newspaper supported by Radicals, but revoked it in 1868 at the request of Thomas W.