The "new" annex to the State House was built between 1902-1905 to replace two 19th century annexes that were poorly built and inadequate in size. The Baltimore architects Baldwin & Pennington designed and supervised the construction of the new annex, which houses both the Senate and the House of Delegates. Both chambers feature unusual black and gold marble in tribute to the colors of the Maryland flag, as well as skylights by the studio of Louis Comfort Tiffany. A black marble line with fossils embedded in it divides the new State House from the old.
Another feature of the annex is the grand staircase to the second floor. On the landing is the monumental painting of Washington Resigning His Commission painted in 1859 by Edwin White. This depicts the scene on December 23, 1783 when General George Washington came before the Continental Congress in the Old Senate Chamber and resigned his commission as commander-in-chief of the Continental Army in order to retire to private life. This pivotal event in the early history of the nation established the principle of the authority of the civilian government over the military.
The new Senate Chamber has four large paintings of Maryland's signers of the Declaration of Independence: Charles Carroll of Carrollton by Thomas Sully and of William Paca, Thomas Stone and Samuel Chase, all by Thomas Beale Bordley. The House of Delegates Chamber features portraits of former speakers of the House of Delegates.