Before the series, he and Gench used to be air-pirates, attacking and stealing things from other airships. It is not said how he and Gench were reformed, and came to work aboard London, however it is likely that he and Gench tried attack a London airship, but instead their airship was shot down and they were captured and taken to London.
Pewsey and Gench assisted Valentine in taking MEDUSA from Pandora Shaw, by flying the Elevator to Oak Island. When Hester was telling Tom Natsworthy about what happened that night, she stated that Pewsey and Gench chased after her, until escaping from them in a rowboat.
When Tom was flying the Jenny Haniver near London, Valentine sent Pewsey and Gench in the Elevator to destroy the Jenny. They fired rockets at the Jenny Haniver, damaging much of the gondola. Tom, however, fires rockets at the Elevator's windows, killing Pewsey and Gench and sending the Elevator crashing onto London. But Tom felt bad about killing Pewsey and Gench after London is destroyed.