Mosby defeated two-term incumbent Baltimore City Councilwoman Belinda K. Conaway by a double-digit margin. This surprising political upset shocked the political establishment and received a lot of attention because it was the first time in almost thirty years where a political challenger beat a seated member of the Baltimore City Council. As a Councilman, Mosby organized over 60 Enough is Enough marches, working with police and community groups to reduce crime and violence in West Baltimore. Seeing how poor health was harming his community, Mosby started the "Get Fit with Councilman Mosby" Challenge, partnering with close to 30 personal trainers, fitness organizations and chefs, the American Heart Association and Y of Central MD to provide free access to fitness and cooking classes. Mosby has long fought for criminal justice reform. As Councilman, he developed and ran a mentoring program for juveniles awaiting trial as adults in the Baltimore City Detention Center. He introduced a law that was passed banning the requirement of criminal records on job applications, which enabled ex-offenders to have a fresh start. He also introduced a law that was passed stopping liquor stores from selling merchandise to children. Mosby arranged for the donation of school supplies for thousands of children, and organized free cultural enriching trips for thousands of children in West Baltimore. In 2012, Mosby appeared on the reality show Kitchen Nightmares, presenting Cafe Hon owner Denise Whiting a Baltimore City resolution.
2015 Baltimore Uprising
During the 2015 Baltimore protests following the death of Freddie Gray, Mosby said that the unrest was "unproductive" but also the result of decades old of lack of investment and socio-economic decline. Mosby's unscripted comments in the middle of the street with protestors, burning buildings, and looters quickly went viral and garnered over two million views in a little over a day. During the interview Mosby also pointed out how the media was quick to call the incident a "riot" but consistently failed to do the same when compared to other incidents, like the 2015 riots in Lexington, Kentucky, after the Kentucky Wildcats lost to the Wisconsin Badgers. That interview would later be used by communication organizations and colleges as an example of staying on message despite surroundings and rapid fire questioning from reporters. Mosby represented District 7 on the Baltimore City Council, where most of the civil unrest occurred.
Bid for mayor
On October 26, 2015, Mosby announced that he was running for mayor of Baltimore. He dropped out of the race on April 13, 2016. When he announced his bid for the mayoral election, Mosby decided to forego a bid for re-election to his seat on the Council. On November 8, 2016, Leon F. Pinkett won his vacated seat on the Council.
