[1][2] Harahan served as a captain in the Union Army during the American Civil War.

[citation needed] Harahan married to Mary Kehoe of New Orleans, Louisiana in 1866.

[3][4] Four children were born of this marriage including his son, William Johnson Harahan, who was born in Nashville, Tennessee, on December 22, 1867, and was twice president of the Chesapeake and Ohio Railway; he died of natural causes in 1937 in Clifton Forge, Virginia.

[5] Harahan's second marriage was to Mary N. Mallory of Montgomery County, Tennessee on April 14, 1899.

They were traveling to a meeting to discuss the building of a railroad bridge across the Mississippi River at Memphis.