The 120th Delaware General Assembly was a meeting of the legislative branch of the state government, consisting of the Delaware Senate and the Delaware House of Representatives. Elections were held the first Tuesday after November 1 and terms began in Dover on the first Tuesday in January. This date was January 6, 1959, which was two weeks before the beginning of the seventh administrative year of Governor J. Caleb Boggs and the third administrative year of David P. Buckson as Lieutenant Governor. In the 120th Delaware General Assembly session, both chambers had a Democratic majority.