Cassidy was appointed to council to fill a casual vacancy on Deagon Ward in 2015, following the resignation of longtime councillor Victoria Newton.
However, this did not happen, and Peter Cumming was elected to the role unopposed.
[5] In September 2019, six months before the 2020 Brisbane City Council election, Cumming stepped down as leader and Cassidy took his place.
[6] On 12 November 2019, he was escorted out of the council chamber after he refused an order to leave for yelling "crock of shit".
[7] Cassidy was re-elected in 2020 with an increased primary and two-party-preferred vote.