During the Civil War, President Abraham Lincoln’s Emancipation Proclamation of 1863 freed slaves in Confederate states but not in the Union state of Maryland. Indeed, 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. A state-wide referendum was held October 12 and 13, 1864, with  special provisions were made to allow soldiers in the field to vote, and Governor Bradford certified the election totals on October 29. The third state constitution, which abolished slavery in Maryland, went into effect November 1, 1864.