Neilson was sworn-in on May 8, 2012. He served on the Children and Youth, and Veterans Affairs and Emergency Preparedness committees.
Neilson entered the race to succeed O'Brien, and won the Democratic primary unopposed. In the special election, he faced Dave Kralle, a long-time aide to O'Brien who served as his Chief of Staff at the end of his legislative tenure. On election day, Neilson defeated Kralle, and will hold the seat until January 2013. He will again face Kralle in the November 2012 general election, this time vying for a full two-year term.
Neilson was sworn into Philadelphia City Council on August 14, 2014 and resigned on June 19, 2015.
In February 2014, former City Council Member Bill Green and was sworn in as the chair of the School Reform Commission. He was nominated by Governor Tom Corbett. In March 2014, Democratic ward Leaders picked Neilson for the City Council special election that would be held in May 2014. Neilson entered the race to succeed Bill Green, and won the special election to defeat Matt Wolfe, a Republican ward leader from West Philadelphia. He later resigned the seat on June 19, 2015.
