Grubb steps up from his position as coach of GB U18s, while Richard Hartmann will continue as under-20s assistant and Dayle Keen has been named as a new assistant coach.
National Development Head Coach, Tony Hand, said: "I would like to thank Slava Koulikov and Aaron Nell who have stepped down from their roles.
"On behalf of Ice Hockey UK, I would like to express our gratitude for all they have done over the past few years.
"I am excited to announce the trio of Martin, Richard and Dayle as the new coaches for the under-20s.
"Martin and Richard have huge experience in the GB junior set-up and both are very talented coaches in their own right.
"Meanwhile, Dayle is a highly-regarded young coach and is well thought of across the UK. I am sure all three will make a great team to take the program forward."
Grubb said: "I’m am very proud and honoured to be able to represent Great Britain again and lead the under-20s team this season.
"There is a talented group of players at that age and I have been able to coach the majority of them at some point in their GB careers, so it will be exciting to work with that group and there will be some difficult decisions as we work towards selecting a team.
"I have a solid base to build on with the excellent work done by Slava and Aaron - and we will be trying to better the bronze medal win from last season.
"I am looking forward to working with Richard and Dayle - and I am sure they will do a good job.
"I would like thank Tony Hand and Ice Hockey UK for allowing me the opportunity to continue working with these players in the GB program."