Not a lot is known about him but he is very timid and easily intimidated. He also is prone to panic when his boss is upset. Soft-spoken and middle-witted he is averagely competent and can come up with good ideas at times, but he is a docile wimp. He is very pitiful but can still be called a villain.
When the Anti-Recess Group took over a military testing site to steal the weather altering laser that was in development in the area, he managed to shut down the alarms, before telling Benedict that the situation is now all clear, before learning that their next move is to covertly take over Third Street School when summer begins. Later on, Fenwick was tasked with finding the principal's office, although he doesn't see what's so significant about it that would necessitate Benedict to find it for him, before Benedict reveals that the reason it is significant for him is because he used to work there.
He is later told off along with the other personnel in regards to the failures regarding the tractor beam (referring to the earlier forced terminated test of the weather altering laser that was unintentionally revealed to T.J. and his gang). He and some scientists also attempted to convince Benedict to relocate due to the school not having enough power to allow for full capacity, although Benedict, driven largely with making sure Third Street was the site of its success due to being fired there, adamantly refused in a infuriated manner.
After it became apparent that T.J. and the others snuck into the school (Mikey was unable to hold in a belch developing inside him, and the vents they were observing in gave way), Fenwick was briefly questioned by Benedict as to who let kids in the school before Benedict screamed for his men to get them, resulting in T.J.'s capture. Later on, after Gretchen managed to black out the lab that used to be the auditorium, Fenwick and some scientists was tasked to fix the fuse (under the belief that it was the result of a blown fuse), although they ended up locked inside of the power room by Gretchen. Having somehow managed to get out and supply a backup generator, they then attempt to proceed with the laser as planned, even with a fight between Benedict's forces and a joint group of students and teachers.
At the end as Fenwick being escorted off to the police car, he asks for Kojak, the Secret Service Look-Alike Agents, the ninjas & the scientists to be set free by saying that he was following Benedict's orders and offers to testify against Benedict for the trial in exchange for leniency. The police officer refuses his offer and furiously arrests him, and even Randall was appalled at the offer, saying "Jeez, what a squealer!"
It was implied that Fenwick was sentenced to lifetime in prison along with Benedict and their men for their crimes.