The Kent-based manager achieved his goal of keeping the club in the National League after taking over a team struggling for form and confidence.
His exit was confirmed on Friday and alongside Jamie Day their pair will leave Holker Street after survival was achieved.
Pennock released a statement to supporters saying his half-a-year in Cumbria was one he loved.
He said: “When I became manager back in October there were plenty of people questioning “what am I going up there for”, but I have really enjoyed my 6 months at what is a great club with some great people.
“The supporters have been incredible and I would like to say a big thank you! You have been brilliant from my first game against Aldershot to backing us in numbers on the final day against Chester.
“Let there be no doubt that your support, particularly on the road as we picked up vital points at places like Aldershot and Bromley, played no small part in helping this club retain its place in the National League.
“I’d also like to say thank you to my staff, to Jamie Day, Grant Holt, Lindsay Davis, Mick Holgate & Dean Scholey for all of their efforts. Thanks also to all of the hardworking staff at the club, both on match days and through the week, who help make the club what it is.
“Barrow is a fantastic club and I hope to come back one day to finish what we started. But until then, I wish you all the best of luck next season and beyond, I’ll be keeping an eye on results come August. Thank you and good luck.”
The Bluebirds’ search for their next manager is already underway, the owners have confirmed.