St. Louis Alderman Antonio French announced his run on Twitter on Thursday.
I'm in. https://t.co/vXYVPrQtnY— Antonio French (@AntonioFrench) October 6, 2016
He must still file paperwork with the state.
French was active during the Ferguson protests, when he frequently shared pictures and videos of clashes between police and protesters.
The announcement comes the day after Police Chief Sam Dotson announced his bid to replace Mayor Francis Slay.
President of the St. Louis Board of Aldermen Lewis Reed and Alderwoman Lyda Krewson are also running.
City treasurer Tishaura Jones and Collector of Revenue Gregory Daly have mailed paperwork to form a committee to run.