Born near Carnesville, Georgia, Sandidge moved to Louisiana and became a planter. He served as colonel in the Mexican War. He served as member of the State house of representatives 1846-1855 and served two years as speaker. He served as delegate to the State constitutional convention in 1852.
Sandidge was elected as a Democrat to the Thirty-fourth and Thirty-fifth Congresses (March 4, 1855-March 3, 1859). He served as chairman of the Committee on Private Land Claims (Thirty-fifth Congress). He served throughout the Civil War as colonel of Bossier Cavalry. Surrendered the archives of the State to the Federal authorities in the absence of Gov. Henry W. Allen. He died in Bastrop, Louisiana, on March 30, 1890.