On January 1, 1863 President Lincoln signed the Emancipation Proclamation. By his “war power” as commander-in-chief, Lincoln declared that all the slaves in Confederate-held territory as of that date were “thenceforward, and forever free.” Excluded from the presidential order were the loyal Border States of Delaware, Maryland, Kentucky, and Missouri; the state of Tennessee (then under Union control); the counties of what would soon become the state of West Virginia, and certain counties in Virginia and Louisiana. The document affirmed that black men would be used in the Union military.
Maryland's Constitution of 1851 had forbidden passage of "any law abolishing the relation of master or slave, as it now exists in this State" (Art. 3, sec. 43). To end slavery, Maryland had to write a new constitution.
Governor Augustus W. Bradford, in his annual message of 1864 to the General Assembly, sought passage of a constitutional convention bill. The predominently Unionist legislature promptly complied, and the electorate approved the call for a convention (Acts of 1864, ch. 5).
Delegates to the Constitutional Convention of 1864 were elected by the voters on April 6, 1864. The convention convened in Annapolis on April 27, 1864, and adjourned on September 6, 1864. The third state constitution, which abolished slavery in Maryland, received approval of the voters on September 18, 1864, and took effect November 1, 1864.