|“||Damn the Clave. We don't need them and their half-breed-tolerating ways.||”|
Having joined the Circle some time before the signing of the Ninth Accords, Blackwell was among those members who fully believed in Valentine and his cause. Because of this faith in their leader, Blackwell did not leave the group and took part in the Uprising. When they failed, however, Blackwell, who did not want to cooperate with the Clave and sell out Valentine, was forced to flee Idris and had since gone into hiding.
Along with Emil Pangborn, Blackwell assisted Valentine in faking his death while he posed as Michael Wayland, "killing" him in sight of Valentine's hiding "son", the boy Valentine had raised as Jonathan Wayland.
In 2007, Blackwell and Pangborn came with Valentine to New York. The pair went to Luke, a former member of the Circle who had been with Valentine's wife, Jocelyn, over the years. They tried to coerce information out of him, about the Mortal Cup and Jocelyn's daughter. During the confrontation, they were seen by Jace and Clary. Jace first mistook them for warlocks because they had been wearing official Accords robes meant for warlocks, ones they had apparently skinned off of dead ones, before he recognized them as the men who "murdered" his father. They left upon Luke's insistence that he did not intend to go against Valentine or hide anything from him.
A few days after, Luke, with his new pack, attacked their hideout, the ruins of Renwick hospital on Roosevelt Island, previously owned by his ancestors and known as Blackwell's Island. There, he and Pangborn were both killed by Luke during a confrontation.
Blackwell was big and burly and had short reddish hair and thick fingers.
- In the original editions of City of Bones, Blackwell's skin appeared dark purple and shiny and stretched over his cheekbones due to dark magic. This was redacted in the repackaged editions.