Its central interior feature is a white marble rotunda, about 100 feet square, with a colored glass skylight above and a marble grand staircase opposite the main entrance. In 1896, a temporary wooden convention hall was erected on the south lawn of City Hall. It housed the Republican conclave which nominated William McKinley for his first term as president.

Construction began on July 19, 1890 and was completed on November 5, 1904. No bonds were issued to finance its construction, which is why it took 14 years to complete the building. The budget was limited at $2 million, but the final cost was only $1,787,159.16.

The exterior of the first story is Missouri pink granite that contrasts with pink-orange Roman brick on the upper floors and buff color sandstone trim located in an irregular pattern around the window openings. The roof is burgundy-red clay tiles.

The building has four floors and a basement level. It was considered fireproof by 1904 standards. It contains 150 rooms: 26 in the basement; 34 rooms each on the first, second, and third floors; and 22 rooms on the fourth floor.

When City Hall was designed, St. Louis had a bicameral form of government similar to the Missouri Legislature. The building originally had chambers and meeting rooms for the House of Delegates and the City Council. The 1914 City Charter eliminated the Council and changed the House of Delegates to the Board of Aldermen. The room that once housed the Council is now the Board of Public Service Chamber, and the Board of Aldermen occupy the House of Delegates chamber and committee rooms. The Mayor´s office remains in its original space on the northeast corner of the second floor.

The clock above the main entrance on Tucker was installed in 1906 and renovated in 2001. The lantern-like central tower, about 80 feet tall, above the Tucker Boulevard entrance and the two smaller spires, each about 19 feet in height, on either side of the tower, were removed in 1936. In the process of reroofing, the structural steel frame of the towers was found to be so corroded that the tower had to be taken down with great care, piece by piece. The public was outraged that the tower was demolished and Mayor Bernard Dickman promised to build a new tower when the city had the money. The replacement cost at the time was estimated to be $10,000. A campaign was started in 1946 to replace the tower and a study was done. It was found to be too expensive and the project was dropped.

The words "City Hall" were engraved in the stone above the doors on the Market, Tucker, and Clark Street entrances. This was done only after the City Art Commission refused to allow Mayor Dickmann to put a neon "City Hall" sign in red, white, and blue above the door.